Several (doc) comments were super outdated or didn't provide enough context.
Some doc comments shoved everything in a single paragraph without respecting
the fact that the first paragraph should be a single sentence because rustdoc
treats these as item descriptions / synopses on module pages.
Most tests involving save-analysis were removed, but I kept a few where
the `-Zsave-analysis` was an add-on to the main thing being tested,
rather than the main thing being tested.
For `x.py install`, the `rust-analysis` target has been removed.
For `x.py dist`, the `rust-analysis` target has been kept in a
degenerate form: it just produces a single file `reduced.json`
indicating that save-analysis has been removed. This is necessary for
rustup to keep working.
Closes#43606.
