Revert "treewide: replace rev with tag"

This reverts commit 65a333600d.

This wasn't tested for correctness with something like fodwatch [0],
and should not have been (self-)merged so quickly, especially without
further review.

It also resulted in the breakage of at least one package [1] (and that's
the one we know of and was caught).

A few packages that were updated in between this commit and this revert
were not reverted back to using `rev`, but other than that, this is a
1:1 revert.

[0]: https://codeberg.org/raphaelr/fodwatch
[1]: https://github.com/NixOS/nixpkgs/pull/396904 / 758551e458

doc/languages-frameworks/javascript.section.md

@@ -194,7 +194,7 @@ buildNpmPackage rec {
   src = fetchFromGitHub {
     owner = "jesec";
     repo = pname;
-    tag = "v${version}";
+    rev = "v${version}";
     hash = "sha256-BR+ZGkBBfd0dSQqAvujsbgsEPFYw/ThrylxUbOksYxM=";
   };