treewide: mostly noop: refer to src.name or similar in sourceRoot where appropriate

[oxij]

Description of changes

This replaces all the uses of sourceRoot = "source";, sourceRoot = "source/subdir";, and similar in package derivations that use the default unpackPhase with sourceRoot = src.name, sourceRoot = "${src.name}/subdir"; and similar.

It also fixes sourceRoot and setSourceRoot description in the docs to match the implementation, and deprecates the old usage in release notes.

The primary motivation for this change is to make #49862 (or its reverse) trivial to implement.

Things done

It's a mostly noop change except for the changes to documentation (which cause nixos-install-tools to be rebuilt).

[oxij]

Rebased onto master to fix a conflict with qrcodegen, it will get rebuilt now as 0164461 started to use preBuild for doing the same thing (without good reason, AFAICS).

[drupol]

I did use finalAttrs in the expression that used them already, I was trying to do the minimal change...

I know, but what I'm saying here is a bit different... I'm saying that we should avoid using rec when finalAttrs can be used.

[AndersonTorres]

The removal of rec can be done in other PRs.

[oxij]

OfBorg seems to be stuck? Pending eval for 20 hours.

[oxij]

@drupol I pushed a new commit that replaces all newly introduced mkDerivation recs with fixpoints. buildRustPackage and buildGoModule do not support this yet, so can't do that there. I consider changing recs that I did not put there to be out of scope of this PR because that's a lot of package-specific work right there. I hope your objection can be withdrawn now?

[drupol]

Excellent, thanks !!!!

[AndersonTorres]

OfBorg seems to be stuck? Pending eval for 20 hours.

aarch64-darwin usually spends days bootstrapping.
Whereas x86_64-darwin dies of timeout :)

[oxij]

Yay! All checks pass, still no conflicts. A prime opportunity to merge. :)

[AndersonTorres]

Except merge conflicts.

Maybe because I burned it up :(

[oxij]

Rebased.

[oxij]

🍻

[oxij]

This now has a continuation in #247977.

[ShamrockLee]

Please take a look at #294334 for yet another cleanup regarding such hard-coding sourceRoot specification.

This is required for #294068, after which non-compliant packages should fail to build, saving future maintenance overhead.