Add doc for project-wide renaming

[jian-lin]

Also add doc for sessionLoading since it is needed by project-wide renaming.

Doc for cabalFormattingProvider is also added. It is not tightly connected to the theme of this PR though.

related: #2193 #3738
closes: #4355

[jian-lin]

ping @fendor

[dschrempf]

Not directly related, but is there a reason why mutipleComponents is not the default? It's cumbersome to define this for every project, isn't it? And it is annoying when you can not jump to a definition in another package of the same project. What are your experiences?

[jian-lin]

Maybe because:

• Allow users to specify whether to use cabal's multi-repl feature #4179 (comment)
• https://well-typed.com/blog/2024/07/hls-multi/#enabling-multi-component-support-in-hls

Not sure if these reasons are outdated though.

Also note that mutipleComponents alone is not enough for project-wide renaming.

[fendor]

is there a reason why mutipleComponents is not the default?

It can be slow without eager component loading, see #4381.
A regression as well: #4431
Also, we have no good way to let the user decide to use eager loading, except a custom hie.yaml.
Once these three issues are solved, I think it should be made the default!

[fendor]

LGTM, thanks for taking care of the documentation!

[fendor]

This PR also closes #4355