[llvm] [NFC]Rename collectPGOFuncNameStrings to collectGlobalVariableNameStrings (PR #70287)

[David Li via llvm-commits]

https://github.com/david-xl commented:

Since both Function and GlobalVariable are subclasses of GlobalObject, perhaps name it collectGlobalObjectNameStrings?

https://github.com/llvm/llvm-project/pull/70287