[clangd] Support pseudo-obj expr, opaque values, and property references in...

[clangd] Support pseudo-obj expr, opaque values, and property references in findExplicitReferences()

Reviewers: ilya-biryukov, dgoldman

Subscribers: MaskRay, jkorous, arphaman, jfb, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D72508