fix: circular dependencies disable all involved extensions

[SychO9]

Changes proposed in this pull request:
Throws an exception wen circular dependencies are found, which prevents the extensions within the circular depdencies fro getting all disabled.

Screenshot
This is an example where I created a circular dependency with emoji, suspend, and likes:

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)
• Related core extension PRs: (Remove if irrelevant)

[askvortsov1]

Should we also reject attempts to enable extensions that would cause circular dependencies?

[SychO9]

That would already be rejected as well, whether the extension being enabled causes the circular dependency. Or whether there is an existing circular dependency with other already enabled extensions (due to an update). The error is thrown.

[askvortsov1]

Ah right, this would run when enabled extensions are persisted. Looks good!