doc: unify and compact some fragments in fs.md

[vsemozhetbyt]

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

Refs: #19898 (comment)

@BridgeAR, @ryzokuken , please, let me know if I am missing some other deviations in format patterns.

There is a questionable case in this doc I've abstained to change: many Sync function descriptions contain notes Returns `undefined`. that are not commonly formalized. If I recall correctly, there were attempts to add formal * Returns: `undefined` all-docs-wide, but they were not adopted. In this case, these notes in Sync function descriptions may stress the specificity of these functions, so I've not deleted them during cleaning some other possible tautology. If they should be deleted, let me know.

[vsemozhetbyt]

CI-lite: https://ci.nodejs.org/job/node-test-pull-request-lite/530/

[ryzokuken]

LGTM, Will rebase mine if this gets landed first.

[BridgeAR]

I just looked through the docs briefly and found the following:

stats.isSymbolicLink() (and above seem to have two "returns").

Returns: {boolean}
Returns true if the fs.Stats object describes a symbolic link.

And besides your findings that some functions note that they return undefined a lot of sync functions do not show any return type at all. I think especially in fs it would be useful to add those consistently.

I also noticed that some Returns foo is actually a second sentence and not a new line, e.g., Synchronous version of fs.futimes(). Returns undefined.

Than again, some functions have a bullet point as return type, e.g., fs.writeSync

[vsemozhetbyt]

This is my thoughts on these, but they are not strong opinions, so if there is some minimal consensus to change this I can do it in a new PR:

1. Sometimes there is a formal return signature and a description for this in next paragraph (if, else, etc ). This is also valid for parameters and options. So maybe all the fs.Stats duplications are just non-formal expanding. But they can be easily merged into above lines,

2. What would we prefer: delete all the Returns `undefined`. or add them where they are missed and unify them? Considering the second whould be inconsistent with the other docs.

3. It seems only functions with defined return values have bullet point returns.

[vsemozhetbyt]

Landed in 809eb27

[vsemozhetbyt]

@nodejs/documentation If anybody has opinions about notes in #20050 (comment), #20050 (comment), and #20050 (comment), please, let us know.