Update ShadowWrangler to iterate through methods using getDeclaredMethods

[hoisie]

Update ShadowWrangler to iterate through methods using getDeclaredMethods

Previously, in ShadowWrangler, shadow method lookup was performed using
ShadowClass.findDeclaredMethod. It was called once to look for an exact match
of a shadow method, and sometimes called again to check for a looseSignatures
match.

There are plans to add new features and capabilities to the way that shadow
methods are matched. For example:

• looseSignatures being replaced with a more minimal
  @classname("internal.type") annotation.
• If the signature of a method changes across SDK levels, we could introduce
  different method names that map to the same method name.

However, to search for methods that cannot be matched using
ShadowClass.findDeclaredMethod, it is required to iterate over all candidate
methods using ShadowClass.findDeclaredMethods.

There were some questions about the performance of using
ShadowClass.findDeclaredMethods + iteration. However, after some preliminary
benchmarks, this approach is surprisingly approximately 25% faster than using
ShadowClass.findDeclaredMethod. It is perhaps due to the internal caching of
ShadowClass.findDeclaredMethods.

With this change, it will be possible to perform more advanced filtering and
searching for methods.

For #8841

[hoisie]

FYI @utzcoz I updated ShadowWrangler to use ShadowClass.getDeclaredMethods and iterate over the methods. Surprisingly it's like 25% faster than calling getDeclaredMethod. So I think using this approach, we can do things like @ClassName for loose signatures, and your method name mapping PR.

[utzcoz]

@hoisie Cool. I can wait your change landing.