feat: JsFunction.withParameter and named captures for triggers

[Artur-]

Adds a JsFunction.withParameter(name, value) primitive that prepends let <name>=$<N>; and appends the value as a capture, so a function body can reference values by name instead of by positional $N:

element.addJsInitializer(JsFunction.of("setup(target)")
        .withParameter("target", someElement));

The new addJsInitializer(JsFunction) overload accepts pre-built JsFunctions; the existing addJsInitializer(String, Object...) form delegates to it, and ElementJsInitializerRegistration now takes the JsFunction directly instead of rebuilding it from a string/array.

Sweeps the trigger/action/input toJs and toPromiseJs bodies to use the new named form so each rendered fragment reads as its own JS:

DomEventTrigger addEventListener(eventName, action) / removeEventListener(...)
CallbackAction channel(source(event))
PromiseAction observer(inner(event), channel)
HandlerInput return event[propertyName]
PropertyInput return target[propertyName]
SetPropertyAction target[propertyName] = source(event)
SignalInput return target[propertyName]
RequestFullscreenAction return target.requestFullscreen()
WriteToClipboardAction writePayload(text(event), html(event))

The companion "// $N = ..." comments are gone — the names in the body now match the captures. Trigger.install's Javadoc example uses the same form so subclasses are pointed at the named API.

Duplicate parameter names, and names that collide with a previously declared withArguments name, are rejected.

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

 1 427 files  ±0   1 427 suites  ±0   1h 23m 2s ⏱️ -5s
10 041 tests +6   9 973 ✅ +6  68 💤 ±0  0 ❌ ±0 
10 513 runs  +6  10 444 ✅ +6  69 💤 ±0  0 ❌ ±0 

Results for commit ebb7b4c. ± Comparison against base commit 792dc9c.

[Legioth]

I'm not sure this is a good idea after all. See
#24385 (comment)