[Clang] Improve error recovery for invalid calls (#136295)
It doesn't make sense that we only build a RecoveryExpr for expressions
with invalid trailing commas. This patch extends it so that we now
always build up a RecoveryExpr whenever the call contains anything
invalid. As a result, we can back out HasTrailingComma.
There is only one diagnostic change as to concepts, where a RecoveryExpr
than an ExprError is now used to model an invalid requires clause, for
which we suggest adding parentheses around it. (This looks like what GCC
diagnoses)
