[CodeCompletion] Fix issue causing the completion status to not be set correctly for pattern completion

We weren’t setting the code completion token status correctly when parsing patterns with code completion tokens.

Because of this, in the added test case, the `searchSubject` gets added as a member of `Foo` twice - once in the first pass and once in the second pass, causing an assertion failure.

Fixes rdar://80575116 [SR-14687]

Author: ahoppen

lib/Parse/ParsePattern.cpp

@@ -1138,7 +1138,7 @@ ParserResult<Pattern> Parser::parsePattern() {
       // code complete anything here -- we expect an identifier.
       consumeToken(tok::code_complete);
     }
-    return nullptr;
+    return makeParserCodeCompletionStatus();
 
   case tok::kw_var:
   case tok::kw_let: {

test/IDE/complete_override.swift

@@ -757,3 +757,13 @@ class SynthesizedConformance5: SynthesizedConformance2 {
 // OVERRIDE_SYNTHESIZED_5-DAG: Decl[Constructor]/Super:                required init(from decoder: Decoder) throws {|};
 // FIXME: 'required init(from decoder: Decoder)' is suggested twice
 }
+
+protocol ProtocolSr14687 {
+  var value: Int { get }
+}
+struct StructSr14687: ProtocolSr14687 {
+  let foo = val, #^MULTI_VAR_DECL_OVERRIDE^#
+// MULTI_VAR_DECL_OVERRIDE:     Begin completions, 1 items
+// MULTI_VAR_DECL_OVERRIDE-DAG: Decl[InstanceVar]/Super:            value: Int;
+// MULTI_VAR_DECL_OVERRIDE:     End completions
+}

validation-test/IDE/crashers_2_fixed/sr14687.swift

@@ -0,0 +1,5 @@
+// RUN: %swift-ide-test -code-completion -source-filename %s -code-completion-token=COMPLETE
+
+class Foo {
+  let searchSubject = Bar<String, #^COMPLETE^#
+}