Code Completion timeouts after migrating `PostifxExprParen` and `PostfixExpr` to solver-based

[ahoppen]

After migrating PostifxExprParen and PostfixExpr completions to solver-based #63717, we are seeing quite a few timeouts. See the XFails in the stress tester for what these are. We should investigate if we can improve things here

rdar://112130870

[ahoppen]

Using this as a catch-all for more timeouts.