feat(ui5-shellbar): add preventable search field clear event

[kgogov]

The cancel button now clears the search field value by default. Previously, the search field value was preserved. To maintain the previous behavior, listen for the search-field-clear event and call preventDefault().

• Add search-field-clear event with preventDefault support
• Change default behavior to clear search field value on cancel
• Separate clearing behavior from closing behavior
• Add comprehensive test coverage for both scenarios

Jira: BGSOFUIPIRIN-6909

[dobrinyonkov]

Looks good overall, just two comments:

1. Let’s mark the new event as experimental for now.
2. BUG: If the event is prevented and the search field isn’t cleared, the field cannot be reopened.

[dobrinyonkov]

This covers a case in how the search opens/collapses. Instead, we should extend it with || !this.showSearchField, so that we also cover the case when the search field is explicitly closed.

To test this, you can type something in the filed and press the search icon - it shouldn't close the filed, the users will instead trigger a search.

The logic here ensures:

• On mobile, the search opens on its own (we don’t interfere).
• If there’s already a value, the search event is responsible for triggering the search (we don’t interfere).
• (the new condition) If the field is closed, we must open it regardless.

It's not well documented, lets add a comment above to have this info in mind when making changes in future, e.g,:

// Decide when to toggle the search field:
// -  On mobile, the search opens on its own (we don’t interfere).
// - If there’s already a value, onSearch is responsible for triggering the search (we don’t interfere)
// - If the field is closed, we must open it regardless.
if (!isPhone() && (!this.search?.value || !this.showSearchField)) {
	this.setSearchState(!this.showSearchField);
}

[dobrinyonkov]

Minor (optional): We could also flip the condition for readability, e.g.:

if (isPhone() || (this.search?.value && this.showSearchField)) {
return;
}

this.setSearchState(!this.showSearchField);

[kgogov]

Thanks for the well-done review! I really didn’t know about this!

[ui5-webcomponents-bot]

🎉 This PR is included in version v2.14.0-rc.7 🎉

The release is available on v2.14.0-rc.7

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