[Clang] Modify Parser::ParseLambdaExpressionAfterIntroducer to check whether...

[Clang] Modify Parser::ParseLambdaExpressionAfterIntroducer to check whether the lambda-declarator is valid

We had a couple of crashes due to invalid lambda trailing return types that
were diagnosed but not treated as errors during parsing. So now in
Parser::ParseLambdaExpressionAfterIntroducer(...) after ActOnStartOfLambdaDefinition(...)
we also check if the lambda-declarator is invalid and if so we end up in ActOnLambdaError(...).

Fixes: https://github.com/llvm/llvm-project/issues/64962
https://github.com/llvm/llvm-project/issues/28679

Differential Revision: https://reviews.llvm.org/D158808