Janitorial: Disparate cleanup tasks

[tbradsha]

This includes a variety of small cleanup tasks I ran across while scouring the codebase.

Proposed changes:

This PR includes the following:

• Remove Phan suppressions: c15703438e, a792185799
• Remove a WP 6.5 polyfill added in #38428: 01bb8aec96
• Remove/updated is_callable checks: 6e6eab821b, 0dd6d173e7, a6fefc374a
• Update two missed instances of setMethods → onlyMethods: d7458f0120
• Update one instance of private static to private const: 3240990ea8
• Add type hinting: 4f834228c6, b0d86091ab
• Switched a packages/changelogger deprecation to a throw: 0674faf185, d143ebe0ae, 2a6feee5ef
• Removed some unneeded CSS: 3bdaac9338
• Added/updated/removed comments: 7842f7df27, 69aed20ea4, 82bfe8e277
• Removed fallbacks in CRM: 565292bd3c
• Removed unreachable logic in CI tool setup: 460e14b650
• Removed unneeded checks in CRM, Super Cache, and Vaultpress: 17b7094bd6, 5fd572037f, f1f7025d91
• Fixed changelogger error when running on macOS: e66c7aa2bd

Other information:

• [ ] Have you written new tests for your changes, if applicable?
• [ ] Have you checked the E2E test CI results, and verified that your changes do not break them?
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Testing instructions:

Do the changes make sense? Are CI checks happy?

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[tbradsha]

No need for composer 2.2 anymore with PHP 7.2 minimum.

Indeed, and the same goes with symfony/console and symfony/process (and probably others). I'm going to defer that to a separate PR, and I'm also not sure the best way to do it... 😅

Looks like I forgot this comment

82bfe8e277

I'd be satisfied if the title and description are changed to encompass general cleanups

Adjusted.