Add required-field support for additional careers portal inputs

[anonymoususer72041]

Note about dependency on #675

This Pull Request currently builds on top of #675.

The dependency is mainly about the address field:

• Single line address instead of textareas in UI #675 makes sure that all address fields are rendered as single-line inputs with a consistent id="address".
• This Pull Request extends the careers portal validation and relies on the address field having a stable 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, e.g.

- `<input-phone-cell req>`
- `<input-phone-home req>`
- `<input-phoneWork req>`
- `<input-email1 req>` / `<input-email2 req>`
- `<input-source req>`
- `<input-employer req>` / `<input-currentEmployer 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).