reflection: use CC.findall instead of _methods_by_ftype

[aviatesk]

Some of reflection functions use _methods_by_ftype, which doesn't account for the overlay method table, leading to the issues reported in #54189.
With this commit, these problems are addressed by switching these reflection functions to use CC.findall, aligning them with the other ones.

• closes OverlayMethodTables "top-level" inference #54189

[vtjnash]

Sgtm

[vchuravy]

Other locations to look at

• julia/base/reflection.jl

  Lines 2191 to 2192 in 31f3976

  	matches = _methods_by_ftype(tt, #=lim=#-1, world)::Vector
  	params = Core.Compiler.OptimizationParams(interp)

• julia/base/compiler/typeinfer.jl

  Lines 1211 to 1212 in 31f3976

  	for match in _methods_by_ftype(t, -1, get_inference_world(interp))::Vector
  	ty = typeinf_type(interp, match::MethodMatch)

• julia/stdlib/InteractiveUtils/src/codeview.jl

  Lines 160 to 161 in 31f3976

  	matches = Base._methods_by_ftype(Base.signature_type(f, tt), #=lim=#-1, world)::Vector
  	for match in matches

By looking for _methods_by_ftype usage in a function that also takes interp

[aviatesk]

Core.Compiler._return_type is very internal to Core.Compiler and is currently supposed to be used by NativeInterpreter only, so I left it as is.

[vchuravy]

Core.Compiler._return_type is very internal to Core.Compiler and is currently supposed to be used by NativeInterpreter only, so I left it as is.

Should the signature reflect that? E.g. AbstractInterpreter to NativeInterpreter?