swift234

[SourceKit] Add test case for crash triggered in swift::Identifier::isOperatorSlow() const

Stack trace:

```
found code completion token A at offset 107
swift-ide-test: /path/to/swift/lib/AST/Identifier.cpp:63: bool swift::Identifier::isOperatorSlow() const: Assertion `res == conversionOK && "invalid UTF-8 in identifier?!"' failed.
8  swift-ide-test  0x0000000000b5b276 swift::Identifier::isOperatorSlow() const + 406
10 swift-ide-test  0x0000000000b7a164 swift::UnqualifiedLookup::UnqualifiedLookup(swift::DeclName, swift::DeclContext*, swift::LazyResolver*, bool, swift::SourceLoc, bool, bool) + 196
11 swift-ide-test  0x000000000095c6ab swift::TypeChecker::lookupUnqualified(swift::DeclContext*, swift::DeclName, swift::SourceLoc, swift::OptionSet<swift::NameLookupFlags, unsigned int>) + 187
12 swift-ide-test  0x0000000000917959 swift::TypeChecker::resolveDeclRefExpr(swift::UnresolvedDeclRefExpr*, swift::DeclContext*) + 121
14 swift-ide-test  0x0000000000ae6353 swift::Expr::walk(swift::ASTWalker&) + 19
15 swift-ide-test  0x0000000000918537 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>) + 119
16 swift-ide-test  0x000000000091efed swift::TypeChecker::getTypeOfExpressionWithoutApplying(swift::Expr*&, swift::DeclContext*, swift::FreeTypeVariableBinding, swift::ExprTypeCheckListener*) + 221
18 swift-ide-test  0x0000000000907c7e swift::getTypeOfCompletionContextExpr(swift::ASTContext&, swift::DeclContext*, swift::Expr*&) + 1150
20 swift-ide-test  0x0000000000865a46 swift::performDelayedParsing(swift::DeclContext*, swift::PersistentParserState&, swift::CodeCompletionCallbacksFactory*) + 230
21 swift-ide-test  0x0000000000774304 swift::CompilerInstance::performSema() + 3316
22 swift-ide-test  0x000000000071cc33 main + 35011
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>:2:1 - line:2:1] RangeText="Á"
```