[clang] [clang-tools-extra] [clang] skip explicit obj param in code complete (PR #146258)

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MythreyaK wrote:

> What about "ExplicitObjectMemberFunction"? It seems that this part of feature has not been tested.

@zwuis yeah. This addresses only the function arg in the inserted snippet, not the member functions. 

_Originally posted by @HighCommander4 in [#109608](https://github.com/llvm/llvm-project/issues/109608#issuecomment-2826555889)_, 

> See also https://github.com/clangd/clangd/issues/2339, another report that boils down to the second of the two problems in the issue description. 

I'm still exploring the code for that, so maybe I'll create a separate PR for it if and when I figure it out. 

https://github.com/llvm/llvm-project/pull/146258