fix: incorrect typings for Modal hide() method

[davwheat]

Changes proposed in this pull request:

The hide() method of the Modal class will have an event passed as the first param when clicking the Modal's close button due to how the onclick handler is set.

Reviewers should focus on:

Should we change the this.hide.bind(this) to () => this.hide() instead of this? Could be breaking, but I'd argue this param was never public API, really.

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.

[askvortsov1]

Should we change the this.hide.bind(this) to () => this.hide() instead of this? Could be breaking, but I'd argue this param was never public API, really.

Is there a use case for using the original mouse event while closing the modal? I don't see one, so this might be preferable to keep things simpler.