This change makes error and warning annotations mandatory in UI tests.
The only exception are tests that use error patterns to match compiler
output and don't have any annotations.
This commit generalizes the existing `async_idents` lint to easily encompass
other identifiers that will be keywords in future editions. The new lint is
called `keyword_idents` and the old `async_idents` lint is registered as renamed
to this new lint.
As a proof of concept the `try` keyword was added to this list as it looks to be
listed as a keyword in the 2018 edition only. The `await` keyword was not added
as it's not listed as a keyword yet.
Closes#53077
