SI-8900 Don't assert !isDelambdafyFunction, it may not be accurate

The implementations of isAnonymousClass, isAnonymousFunction,
isDelambdafyFunction and isDefaultGetter check if a specific substring
(eg "$lambda") exists in the symbol's name.

SI-8900 shows an example where a class ends up with "$lambda" in its
name even though it's not a delambdafy lambda class. In this case the
conflict seems to be introduced by a macro. It is possible that the
compiler itself never introduces such names, but in any case, the
above methods should be implemented more robustly.

This commit is band-aid, it fixes one specific known issue, but there
are many calls to the mentioned methods across the compiler which
are potentially wrong.

Thanks to Jason for the test case!
Merge pull request #4049 from lrytz/t8900

SI-8900 Don't assert !isDelambdafyFunction, it may not be accurate