[LiveComponent] Return StimulusAttributes from live_action() so it can be spread in a Twig component tag

[Amoifr]

Q	A
Bug fix?	yes
New feature?	no
Issues	Fix #3413
License	MIT

Today, live_action() casts its return value to a string, which prevents it from being spread into a Twig component tag:

{# ❌ doesn't work: the spread receives a plain string #}
<twig:Table:Head {{ ...live_action('sort', {sortBy: 'id'}) }}>

stimulus_action() already returns a StimulusAttributes object (which is both \Stringable and \IteratorAggregate), so the same call written against it does work. The asymmetry was pointed out by @squrious in the issue discussion.

This PR aligns live_action() with stimulus_action() by returning the same StimulusAttributes object directly. Existing usages remain unaffected because Twig calls __toString() automatically when rendering the value (e.g. <button {{ live_action('save') }}>), and the helper is marked @internal on the PHP side.

The existing LiveComponentRuntimeTest::testGetLiveAction is adapted to cast the value to string for the equality assertion and gains a new assertInstanceOf to lock the return type.

[Kocal]

For 3.x, 2.x is not maintained anymore

[Amoifr]

Done, rebased onto 3.x and re-targeted the PR. Thanks @Kocal! 🙏

[github-actions]

📊 Packages dist files size difference

Thanks for the PR! Here is the difference in size of the packages dist files between the base branch and the PR.
Please review the changes and make sure they are expected.

File	Before (Size / Gzip)	After (Size / Gzip)
LazyImage
controller.d.ts	395 B / 257 B	Removed
controller.js	904 B / 457 B	Removed
Map
abstract_map_controller.d.ts	7.6 kB / 1.49 kB	7.29 kB-4% 📉 / 1.46 kB-2% 📉
abstract_map_controller.js	4.92 kB / 1.4 kB	4.65 kB-5% 📉 / 1.26 kB-10% 📉
Map (Bridge Google)
map_controller.d.ts	10.56 kB / 1.92 kB	10.26 kB-3% 📉 / 1.9 kB-1% 📉
map_controller.js	12.9 kB / 3.19 kB	11.25 kB-13% 📉 / 2.84 kB-11% 📉
Map (Bridge Leaflet)
map_controller.d.ts	9.92 kB / 1.84 kB	9.61 kB-3% 📉 / 1.81 kB-2% 📉
map_controller.js	12.45 kB / 3.36 kB	11.38 kB-9% 📉 / 3.17 kB-6% 📉
Svelte
components.d.ts	200 B / 150 B	Removed
components.js	46 B / 69 B	Removed
loader.d.ts	435 B / 217 B	Removed
loader.js	553 B / 313 B	Removed
register_controller.d.ts	384 B / 235 B	Removed
register_controller.js	531 B / 303 B	Removed
render_controller.d.ts	629 B / 353 B	Removed
render_controller.js	1.05 kB / 493 B	Removed
Swup
controller.d.ts	1012 B / 360 B	Removed
controller.js	1.71 kB / 653 B	Removed
TogglePassword
controller.d.ts	896 B / 355 B	Removed
controller.js	2.64 kB / 1.07 kB	Removed
style.min.css	312 B / 218 B	Removed
Turbo
mercure_stream_source_element.d.ts	Added	11 B / 66 B
mercure_stream_source_element.js	Added	1.06 kB / 484 B
turbo_stream_controller.js	1.11 kB / 545 B	1.47 kB+32% 📈 / 721 B+32% 📈
Typed
controller.d.ts	1.9 kB / 501 B	Removed
controller.js	1.8 kB / 638 B	Removed