[clang] [Coverage] Handle array decomposition correctly (PR #88881)

[Andrey Ali Khan Bolshakov via cfe-commits]

bolshakov-a wrote:

> But anyway, I think we end up doing the right thing automatically if you ignore non-unique OpaqueValueExprs.

The problem is that there is no initializing "common expression" in the AST besides non-unique `OpaqueValueExpr`, hence some code handling `ArrayInitLoopExpr` should be written so as not to lose it at all.

@chapuni, @gulfemsavrun, @evodius96, @vedantk, please clarify: should or should not the implicit stuff be traversed here, particularly for array element initialization?

https://github.com/llvm/llvm-project/pull/88881