Const suggestion check: an alias of a deduced parameter type keeps the suggestion not checked #250

Follow-up of #217 and #239 (final review, M1).

With --experimental-const-suggestion-check, a suggestion stays "not checked" when the parameter's type reaches a local through an alias of a deduced type, while the same code without the alias is checked:

int direct(int* p)
{
    decltype(p) q = p;
    return *q;
}
int aliased(int* p)
{
    using P = decltype(p);
    P q = p;
    return *q;
}

• direct: checked in the analyzed files only.
• aliased: not checked with Clang: the rewrite also changes the type of q (a.cpp:9).

The scope step (§5.6, D19) tells the written form from the deduced part, but it does not follow a typedef or an alias declaration whose type is itself deduced from a planned parameter (writtenForm in src/analysis/ConstSuggestionFacts.cpp), so q's type counts as written by the rewrite.

Effect: a suggestion that could be shown valid is kept as not checked. That is conservative; no verdict is wrong.