[clang] [clang-tools-extra] [clang] Make `InitListExpr::isExplicit()` work (PR #195175)

[Andrey Ali Khan Bolshakov via cfe-commits]

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bolshakov-a wrote:

Probably, makes sense to prevent some flaky bugs, but it should eventually be set to some value during deserialization.

https://github.com/llvm/llvm-project/pull/195175