Reland: [clang] Implement evaluation context for checking template parameters

[mizvekov]

Instead of manually adding a note pointing to the relevant template parameter to every relevant error, which is very easy to miss, this patch adds a new instantiation context note, so that this can work using RAII magic.

This fixes a bunch of places where these notes were missing, and is more future-proof.

Some diagnostics are reworked to make better use of this note:

• Errors about missing template arguments now refer to the parameter which is missing an argument.
• Template Template parameter mismatches now refer to template parameters as parameters instead of arguments.

It's likely this will add the note to some diagnostics where the parameter is not super relevant, but this can be reworked with time and the decrease in maintenance burden makes up for it.

This bypasses the templight dumper for the new context entry, as the tests are very hard to update.

This depends on #125453, which is needed to avoid losing the context note for errors occuring during template argument deduction.

Original PR: #126088

[mizvekov]

Keeping in draft form while I investigate the performance regression reported here: #126088 (comment)