[SourceKit] Add test case for crash triggered in swift::constraints::Solution::resolveLocatorToDecl(swift::constraints::ConstraintLocator*) const

Stack trace:

```
found code completion token A at offset 145
swift-ide-test: /path/to/swift/lib/Sema/CSApply.cpp:90: swift::Type swift::constraints::Solution::computeSubstitutions(swift::Type, swift::DeclContext *, swift::Type, swift::constraints::ConstraintLocator *, SmallVectorImpl<swift::Substitution> &) const: Assertion `openedTypes != OpenedTypes.end() && "Missing opened type information"' failed.
9  swift-ide-test  0x0000000000acae49 swift::constraints::Solution::resolveLocatorToDecl(swift::constraints::ConstraintLocator*) const + 1593
10 swift-ide-test  0x0000000000a12acb swift::TypeChecker::getTypeOfExpressionWithoutApplying(swift::Expr*&, swift::DeclContext*, swift::ConcreteDeclRef&, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*) + 443
12 swift-ide-test  0x0000000000a4dd73 swift::getTypeOfCompletionContextExpr(swift::ASTContext&, swift::DeclContext*, swift::CompletionTypeCheckKind, swift::Expr*&, swift::ConcreteDeclRef&) + 691
16 swift-ide-test  0x0000000000c5ade4 swift::Decl::walk(swift::ASTWalker&) + 20
17 swift-ide-test  0x0000000000caf36e swift::SourceFile::walk(swift::ASTWalker&) + 174
18 swift-ide-test  0x0000000000cae67f swift::ModuleDecl::walk(swift::ASTWalker&) + 95
19 swift-ide-test  0x0000000000c851f4 swift::DeclContext::walkContext(swift::ASTWalker&) + 180
20 swift-ide-test  0x00000000009884f8 swift::performDelayedParsing(swift::DeclContext*, swift::PersistentParserState&, swift::CodeCompletionCallbacksFactory*) + 136
21 swift-ide-test  0x00000000008388f1 swift::CompilerInstance::performSema() + 3697
22 swift-ide-test  0x00000000007d9111 main + 42417
Stack dump:
0.	Program arguments: swift-ide-test -code-completion -code-completion-token=A -source-filename=<INPUT-FILE>
1.	While walking into decl 'b' at <INPUT-FILE>:4:1
2.	While type-checking expression at [<INPUT-FILE>:4:8 - line:4:8] RangeText="b"
```

Author: practicalswift

validation-test/IDE/crashers/103-swift-constraints-solution-resolvelocatortodecl.swift

@@ -0,0 +1,4 @@
+// RUN: not --crash %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+// REQUIRES: asserts
+protocol b
+func b{b#^A^#