[SourceKit] Add test case for crash triggered in swift::constraints::ConstraintGraph::Change::addedTypeVariable(swift::TypeVariableType*)

Stack trace:

```
found code completion token A at offset 142
swift-ide-test: /path/to/swift/lib/Sema/ConstraintGraph.cpp:50: std::pair<ConstraintGraphNode &, unsigned int> swift::constraints::ConstraintGraph::lookupNode(swift::TypeVariableType *): Assertion `impl.getGraphIndex() < TypeVariables.size() && "Out-of-bounds index"' failed.
7  swift-ide-test  0x0000000000ab9080 swift::constraints::ConstraintGraph::Change::addedTypeVariable(swift::TypeVariableType*) + 0
8  swift-ide-test  0x0000000000abab32 swift::constraints::ConstraintGraph::addConstraint(swift::constraints::Constraint*) + 130
9  swift-ide-test  0x0000000000ac5d96 swift::constraints::ConstraintSystem::addConstraint(swift::constraints::Constraint*, bool, bool) + 246
10 swift-ide-test  0x00000000009dc750 swift::isExtensionApplied(swift::DeclContext&, swift::Type, swift::ExtensionDecl const*) + 944
16 swift-ide-test  0x0000000000a691f0 swift::TypeChecker::performTypoCorrection(swift::DeclContext*, swift::DeclRefKind, swift::Type, swift::DeclName, swift::SourceLoc, swift::OptionSet<swift::NameLookupFlags, unsigned int>, swift::LookupResult&, unsigned int) + 272
18 swift-ide-test  0x0000000000aebe63 swift::constraints::ConstraintSystem::diagnoseFailureForExpr(swift::Expr*) + 1987
19 swift-ide-test  0x0000000000af1a00 swift::constraints::ConstraintSystem::salvage(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::Expr*) + 4320
20 swift-ide-test  0x0000000000a128cf swift::TypeChecker::solveForExpression(swift::Expr*&, swift::DeclContext*, swift::Type, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem&, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 431
21 swift-ide-test  0x0000000000a1536e swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem*) + 942
24 swift-ide-test  0x0000000000aeb71b swift::constraints::ConstraintSystem::diagnoseFailureForExpr(swift::Expr*) + 123
25 swift-ide-test  0x0000000000af1a00 swift::constraints::ConstraintSystem::salvage(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::Expr*) + 4320
26 swift-ide-test  0x0000000000a128cf swift::TypeChecker::solveForExpression(swift::Expr*&, swift::DeclContext*, swift::Type, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem&, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 431
27 swift-ide-test  0x0000000000a1536e swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem*) + 942
30 swift-ide-test  0x0000000000aeb706 swift::constraints::ConstraintSystem::diagnoseFailureForExpr(swift::Expr*) + 102
31 swift-ide-test  0x0000000000af1a00 swift::constraints::ConstraintSystem::salvage(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::Expr*) + 4320
32 swift-ide-test  0x0000000000a128cf swift::TypeChecker::solveForExpression(swift::Expr*&, swift::DeclContext*, swift::Type, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem&, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 431
33 swift-ide-test  0x0000000000a1536e swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem*) + 942
38 swift-ide-test  0x0000000000aeb706 swift::constraints::ConstraintSystem::diagnoseFailureForExpr(swift::Expr*) + 102
39 swift-ide-test  0x0000000000af1a00 swift::constraints::ConstraintSystem::salvage(llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::Expr*) + 4320
40 swift-ide-test  0x0000000000a128cf swift::TypeChecker::solveForExpression(swift::Expr*&, swift::DeclContext*, swift::Type, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem&, llvm::SmallVectorImpl<swift::constraints::Solution>&, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>) + 431
41 swift-ide-test  0x0000000000a1536e swift::TypeChecker::typeCheckExpression(swift::Expr*&, swift::DeclContext*, swift::TypeLoc, swift::ContextualTypePurpose, swift::OptionSet<swift::TypeCheckExprFlags, unsigned int>, swift::ExprTypeCheckListener*, swift::constraints::ConstraintSystem*) + 942
43 swift-ide-test  0x0000000000a9ab56 swift::TypeChecker::typeCheckTopLevelCodeDecl(swift::TopLevelCodeDecl*) + 134
44 swift-ide-test  0x0000000000a51897 swift::typeCheckTopLevelCodeDecl(swift::TopLevelCodeDecl*) + 647
47 swift-ide-test  0x000000000098ac31 swift::performDelayedParsing(swift::DeclContext*, swift::PersistentParserState&, swift::CodeCompletionCallbacksFactory*) + 305
48 swift-ide-test  0x00000000008393f1 swift::CompilerInstance::performSema() + 3697
49 swift-ide-test  0x00000000007d9894 main + 42916
Stack dump:
0.	Program arguments: swift-ide-test -code-completion -code-completion-token=A -source-filename=<INPUT-FILE>
1.	While type-checking expression at [<INPUT-FILE>:3:1 - line:4:2] RangeText="assert(Range.b
v"
2.	While type-checking expression at [<INPUT-FILE>:3:7 - line:4:2] RangeText="(Range.b
v"
3.	While type-checking expression at [<INPUT-FILE>:3:8 - line:3:14] RangeText="Range.b"
4.	While type-checking expression at [<INPUT-FILE>:3:8 - line:3:14] RangeText="Range.b"
```

Author: practicalswift

validation-test/IDE/crashers/109-swift-constraints-constraintgraph-change-addedtypevariable.swift

@@ -0,0 +1,4 @@
+// RUN: not --crash %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+// REQUIRES: asserts
+assert(Range.b
+v#^A^#