Fixes: #16922
This change updates our analyzers that need access to the symbols to use
`IOperation` where possible. Using syntax analysis for this kind of
analyzer has worse performance. These analyzers run on generated code,
which can include EF migrations, the design of which amplifies these
effects.
On the path to this, I also added support for a few more cases that
operations make easy. Since we're doing this anyway, I want to have
confidence that we're checking everything (within reason). In some cases
the diagnostic experience changed a bit (including more of the
declaration/code) - I felt like all of these were OK changes. Given the
kinds of error message reported by the analyzers "don't use that type"
it seems like it's still a good enough experience without
micro-optimizing all of the locations.
a159473c57