[Clang] Fix dependence handling of nttp for variable templates

[LYP951018]

The dependence of a template argument is not only determined by the argument itself, but also by the type of the template parameter:

Furthermore, a non-type template-argument is dependent if the corresponding non-type template-parameter is of reference or pointer type and the template-argument designates or points to a member of the current instantiation or a member of a dependent type.

For example:

struct A{};

template <const A& T>
const A JoinStringViews = T;

template <int V>
class Builder {
public:
    static constexpr A Equal{};
    static constexpr auto Val = JoinStringViews<Equal>;
};

The constant expression Equal is not dependent, but because the type of the template parameter is a reference type and Equal is a member of the current instantiation, the template argument of JoinStringViews<Equal> is actually dependent, which makes JoinStringViews<Equal> dependent.

When a template-id of a variable template is dependent, CheckVarTemplateId will return an UnresolvedLookupExpr, but UnresolvedLookupExpr calculates dependence by template arguments only (the ConstantExpr Equal here), which is not dependent. This causes type deduction to think that JoinStringViews<Equal> is OverloadTy and treat it as a function template, which is clearly wrong.

This PR adds a KnownDependent parameter to the constructor of UnresolvedLookupExpr. After canonicalization, if CanonicalConverted contains any dependent argument, KnownDependent is set to true. This fixes the dependence calculation of UnresolvedLookupExpr for dependent variable templates.

Fixes #65153 .

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[LYP951018]

@erichkeane @cor3ntin could you review this PR, please? I’m not a collaborator, so I could not add reviewers by myself.

[erichkeane]

This needs a release note, else I think it is OK.

[LYP951018]

@erichkeane could you help me merge this PR please? I could not merge it by myself because I don't have write access to the repo

[shafik]

A couple of nitpicks

[shafik]

/*KnownInstantiationDependent=*/false, /*KnownContainsUnexpandedParameterPack=*/false

to be consistent with bugprone-argument-comment

[shafik]

/*RequiresADL=*/true