feat: add required-field support for additional careers portal inputs

[anonymoususer72041]

Note about dependency on #675

This Pull Request is currently stacked on top of #675.

The overlap is mainly about the address field:

• feat: introduce address2 and replace address textareas with inputs #675 changes the address fields to use single-line <input> elements with a consistent id="address", including the careers portal apply templates.
• This Pull Request builds on that change and extends the careers portal validation. The updated _makeApplyValidator() assumes that <input-address> renders an element with id="address" so that <input-address req> can be validated safely.

Summary

Extend _makeApplyValidator() in modules/careers/CareersUI.php so more input placeholders can be configured as required via the req marker in the careers portal template:

- <input-phone-cell req>
- <input-phone-home req>
- <input-best-time-to-call req>
- <input-bestTimeToCall req>
- <input-email2 req>
- <input-source req>
- <input-employer req>
- <input-resumeUpload req>
- <input-eeo-gender req>
- <input-eeo-race req>
- <input-eeo-veteran req>
- <input-eeo-disability req>

Motivation

OpenCATS already supports a small set of required fields in the careers portal by looking for markers like <input-address req> in the template and generating a JavaScript applyValidate() function accordingly.

However, a number of input placeholders were not "req-aware" and could not be configured as required fields even though they are important in real-world setups (e.g. mobile phone number or resume upload).

This Pull Request extends the existing mechanism in a backwards-compatible way so that careers portal templates can opt into stricter validation where needed by simply adding the req marker to the relevant placeholders.

[anonymoususer72041]

This Pull Request also addresses issue #354.

[RussH]

This PR appears to be built on top of #675 and still includes the single-line address refactor. As noted in my review of #675, this format doesn't work for international addresses (UK building/suite lines). I recommend pausing this until the address field approach in #675 is resolved.

[anonymoususer72041]

@anonymoususer72041 happy to merge this based on your comments above, let me know when #697 is updated and ready, and I'll do them both at the same time.

@RussH done