[demangler] Fold expressions of .* and ->*

(Exitingly) a fold expression's operators include .* and ->*, but we
failed to demangle them as we categorize those as MemberExprs, not
BinaryExprs.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D123305

GitOrigin-RevId: ed2d4da732006d76e2f7b4315a2056b2d7b2f15c
2 files changed