Fix Issue 10602 - Error should state why wrong template lambda doesn'…

[ntrel]

…t match expected function type

Also add ~~globals.errorBuf~~ ~~ErrorSinkBuffer~~ to divert gagged errors. (This will also be useful for another pull I'm working on).

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	10602	normal	Error should state why wrong template lambda doesn't match expected function type

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#15544"

[ntrel]

@RazvanN7 @maxhaton Perhaps (separately) refactoring ~~TypeFunction.callMatch~~ FuncExp.matchType to take an ErrorSink would help? I'm looking at doing that.