Rewrite Button to Typescript

[davwheat]

Progresses #3533, #3364

Changes proposed in this pull request

Button:

• Prefer aria-label over title
• Don't duplicate button content to title attribute
  • This has no effect on a11y. Content of nodes is preferred over title attributes by screen readers.
• Warn in debug mode if button has no accessible content
• Use modern JS/TS syntax (||=, spread, etc)

Others:

• Add debug warning helper: fires console.warn, but only when the forum is in debug mode. Can help to inform extension developers of possible issues with their JS code.
• Update TextEditorButton to work with changes that prefer aria-label

Reviewers should focus on

Is anything else affected by the preferring of aria-label as opposed to title? Most likely components that deeply interact with Button and those which extend it.

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).

Required changes

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

[tankerkiller125]

I think the warning message requires a very slight re-wording so that it isn't confusing, otherwise it looks good to me.

[dsevillamartin]

The warning will be logged every time the button redraws... I think it'd be good to only do it once per element, but that'd probably be outside the scope of this PR.

[davwheat]

I couldn't think of a better way to handle that, to be honest, without risking the checks not working correctly. Things like this.element aren't defined in oninit as far as I'm aware, meaning we can't check if the Tooltip component has set an aria-label attribute.

[dsevillamartin]

I couldn't think of a better way to handle that, to be honest, without risking the checks not working correctly. Things like this.element aren't defined in oninit as far as I'm aware, meaning we can't check if the Tooltip component has set an aria-label attribute.

It's defined in Component.oncreate(), I believe. Warning in oncreate should do the trick.