[2.x] fix: prevent search modal from opening when clear button is clicked

[huoxin233]

Fixes #4593

Changes proposed in this pull request:

The .Search div in AbstractGlobalSearch has an onclick handler that opens the search modal. When the clear button inside the Input component is clicked, the event bubbles up to this handler, causing the search modal to open immediately after clearing the value.

This PR adds a guard in the onclick handler to check if the click originated from within the .Input-clear element and short-circuit before opening the modal.

Found a better solution
This PR modifies the Input component to call e.stopPropagation() inside the clear button's onclick handler. This will prevent the click from bubbling up to any parent container.

Reviewers should focus on:

Screenshot

Before:

PixPin_2026-04-20_23-21-23.mp4

After:

PixPin_2026-04-21_01-19-22.mp4

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)