Issue/21322 rename apptheme

[nbradbury]

Fies #21322

This PR renames AppTheme to AppThemeM2 to clarify that it's the Material2 theme and deprecates it in favor of using AppThemeM3 for new composables. Although a large number of files are changed by this PR, there are no changes to logic - it's a simple rename only.

Note: #21318 should be merged first.

[dangermattic]

	2 Warnings
:warning:	View files have been modified, but no screenshot or video is included in the pull request. Consider adding some for clarity.
:warning:	This PR is larger than 300 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

	1 Message
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Generated by :no_entry_sign: Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr21326-8ad85f9
	Commit	8ad85f951830ec31fad75089a8b4ccd8d3aae760
	Direct Download	jetpack-prototype-build-pr21326-8ad85f9.apk

Note: Google Login is not supported on these builds.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.7% Duplication on New Code

See analysis details on SonarCloud