Like concepts checking, a trailing return type of a lambda
in a dependent context may refer to captures in which case
they may need to be rebuilt, so the map of local decl
should include captures.
This patch reveal a pre-existing issue.
this is always recomputed by TreeTransform.
*this (like all captures) only become const
after the parameter list.
However, if try to recompute the value of this (in a parameter)
during template instantiation while determining the type of the call operator,
we will determine it to be const (unless the lambda is mutable).
There is no good way to know at that point that we are in a parameter
or not, the easiest/best solution is to transform the type of this.
Note that doing so break a handful of HLSL tests.
So this is a prototype at this point.
Fixes #65067
Fixes #63675
Wonder if LambdaScopeForCallOperatorInstantiationRAII should just inherit from `FunctionScopeRAII? Am I missing why not?