feat: allow macOS apps to set activation policies

[codebytere]

Description of Change

Closes #21970.

Right now, we allow users access to some dock functionality by hooking into pretty low-level components, but that can cause bugs as evidenced here, here, and here. For apps that want to set more clear and understandable app activation policies, this new small function on app, setActivationPolicy, should allow them to do that without adding much API maintenance or surface area for bugs.

Alternatives considered:

• Apps can set the LSUIElement value to indicate that their app is an agent app that runs in the background, but that's not intuitive by comparison

cc @zcbenz @MarshallOfSound @ckerr

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• relevant documentation is changed or added
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Added the ability to set app activation policy on macOS.

[zcbenz]

The API looks straightforward 👍 .

[codebytere]

Linux failures are unrelated - see #22033.

[release-clerk]

Release Notes Persisted

Added the ability to set app activation policy on macOS.