[clang][ASTMatchers] Fix forEachArgumentWithParam* for deducing "this" operator calls (#84887)

This is a follow-up commit of #84446.
In this patch, I demonstrate that `forEachArgumentWithParam` and
`forEachArgumentWithParamType` did not correctly handle the presence of
the explicit object parameter for operator calls.

Prior to this patch, the matcher would skip the first (and only)
argument of the operator call if the explicit object param was used.

Note that I had to move the definition of
`isExplicitObjectMemberFunction`, to be declared before the matcher I
fix to be visible.

I also had to do some gymnastics for passing the language standard
version command-line flags to the invocation as
`matchAndVerifyResultTrue` wasn't really considered for non-c++11 code.
See the that it always prepends `-std=gnu++11` to the command-line
arguments. I workarounded it by accepting extra args, which get
appended, thus possibly overriding the hardcoded arguments.

I'm not sure if this qualifies for...