feat: Add missing gradient functions

[Aiving]

Closes #773, also closes #774

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 67.21311% with 100 lines in your changes missing coverage. Please review.

Project coverage is 73.90%. Comparing base (c3821a3) to head (9b55129). Report is 2 commits behind head on main.

Files	Patch %	Lines
crates/state/src/values/gradient.rs	44.27%	73 Missing :warning:
crates/core/src/elements/rect.rs	0.00%	18 Missing :warning:
crates/state/src/values/fill.rs	33.33%	4 Missing :warning:
crates/core/src/node.rs	0.00%	3 Missing :warning:
crates/devtools/src/tabs/style.rs	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #776 +/- ## ========================================== - Coverage 73.94% 73.90% -0.05% ========================================== Files 201 201 Lines 21172 21453 +281 ========================================== + Hits 15655 15854 +199 - Misses 5517 5599 +82 ```

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[Aiving]

@marc2332 I think it is now ready for workflow approval and, if all goes well, for review too.

[Aiving]

Oh, okay!

[Aiving]

LGTM. Could you update the gradient example to showcase the new two methods tho?

done!

[Aiving]

I was thinking about having 1 example instead of 3 hehe

done!