Account for CORINFO_HELP_VIRTUAL_FUNC_PTR in GT_LABEL; avoid double resolving (#87395)

Account for CORINFO_HELP_VIRTUAL_FUNC_PTR in GT_LABEL; avoid double resolving (#87395)

In the helper-based tailcall mechanism it is possible that we expand the
target call into two actual calls: first, a call to
CORINFO_HELP_VIRTUAL_FUNC_PTR to compute the target, and second a call
to that target. We were not taking into account that the return address
needed for the tailcall mechanism needs to be from the second call.

In this particular case the runtime does not request the JIT to pass the
target; that means we end up resolving the target from both the caller
and from the CallTailCallTarget stub. Ideally the JIT would be able to
eliminate the CORINFO_HELP_VIRTUAL_FUNC_PTR call in the caller since it
turns out to be unused, but that requires changes in DCE (and is
somewhat non-trivial, as we have to preserve a null-check).

A simpler way to improve the case is to just change the runtime to
always request the target from the JIT for GVMs, which means the
CallTailCallTarget stub no longer needs to resolve it. That also has the
effect of fixing the original issue, but I have left the original fix in
as well.

Fix #87393