Allow customization of 'Now' and 'Clear' buttons in alt-date widget

[amiuhle]

Reasons for making this change

The Now and Clear buttons on the alt-date widget are static. This adds support for customization via ui:options.

Checklist

• [x] I'm updating documentation
  • [x] I've checked the rendering of the Markdown text I've added
• [x] I'm adding or updating code
  • [x] I've added and/or updated tests
  • [x] I've updated docs if needed
  • [x] I've run npm run cs-format on my branch to conform my code to prettier coding style
• [x] I'm adding a new feature
  • [x] I've updated the playground with an example use of the feature

[amiuhle]

I'll update the docs and add a playground example, just wanted to make sure this gets merged / is the right approach first.

[amiuhle]

I also added the possibility to edit the placeholders for the dropdowns.

[glasserc]

The code seems OK, but I guess I would bikeshed the names of the options. How about options.placeholders.year or options.yearPlaceholder instead of options.year?

[amiuhle]

I can do that, I'd prefer the namespaced options.placeholders.year option. How about the "Now" and "Clear" buttons? options.labels?

[r4j4h]

I will try and remember to update my TimeWidget and AltTimeWidget MRs to support this once we agree on the naming convention.

[epicfaace]

@amiuhle -- are you still working on this? If so, could you update the names of the options and also add some tests? I like options.placeholders and options.labels as you suggested.

[swetapatnaik]

Is there an example for this? Or can you say what should be the code.

[amiuhle]

@epicfaace Totally forgot about this, I'll have a look next week.

[epicfaace]

@amiuhle just bumping this!

[amiuhle]

@epicfaace I put the placeholders / labels into namespaces, added docs and a placeholder example and added some tests.

[amiuhle]

Any chance this can be merged?

[heath-freenome]

Closing in favor of #3460