Move themesPage to ThemeController

Noob here: I tried to spin this up in DrupalPod with D11, but there are issues with Composer Dependencies. Can anyone assist?

--------------------

Problem 1
- Root composer.json requires drupal/core == 11.9999999.9999999.9999999-dev (exact version match), it is satisfiable by drupal/core[11.x-dev] from composer repo (https://repo.packagist.org) but drupal/core[dev-3220216-move-themespage-to, 10.2.x-dev] from path repo (repos/drupal/core) has higher repository priority. The packages from the higher priority repository do not match your constraint and are therefore not installable. That repository is canonical so the lower priority repo's packages are not installable. See https://getcomposer.org/repoprio for details and assistance.

Problem 2
- Root composer.json requires drupal/core-project-message == 11.9999999.9999999.9999999-dev (exact version match), it is satisfiable by drupal/core-project-message[11.x-dev] from composer repo (https://repo.packagist.org) but drupal/core-project-message[dev-3220216-move-themespage-to, 10.1.x-dev] from path repo (repos/drupal/composer/Plugin/ProjectMessage) has higher repository priority. The packages from the higher priority repository do not match your constraint and are therefore not installable. That repository is canonical so the lower priority repo's packages are not installable. See https://getcomposer.org/repoprio for details and assistance.

Problem 3
- Root composer.json requires drupal/core-recommended == 11.9999999.9999999.9999999-dev -> satisfiable by drupal/core-recommended[11.x-dev].
- drupal/core-recommended 11.x-dev requires drupal/core 9.3.x-dev -> satisfiable by drupal/core[9.3.x-dev] from composer repo (https://repo.packagist.org) but drupal/core[dev-3220216-move-themespage-to, 10.2.x-dev] from path repo (repos/drupal/core) has higher repository priority. The packages from the higher priority repository do not match your constraint and are therefore not installable. That repository is canonical so the lower priority repo's packages are not installable. See https://getcomposer.org/repoprio for details and assistance.

Problem 4
- Root composer.json requires drupal/core-dev == 11.9999999.9999999.9999999-dev -> satisfiable by drupal/core-dev[11.x-dev].
- drupal/core-dev 11.x-dev requires symfony/browser-kit ^4.4 -> found symfony/browser-kit[v4.4.0-BETA1, ..., 4.4.x-dev] but these were not loaded, likely because it conflicts with another require.

This doesn't feel like a novice issue to me - I'm removing the tag.

-mike

mstrelan → changed the visibility of the branch 11.x to hidden.

mstrelan → changed the visibility of the branch move-theme-page to hidden.

Rerolled for 11.x and added BC layer. Added @todo items for deprecations.

Not sure we really need to deprecate and provide BC since controllers are not API. But there is at least one module in contrib overriding this class and this method - https://git.drupalcode.org/project/multi_theme/-/blob/1.0.x/src/Controll...

Maybe we can just remove the properties and trait only deprecate the themesPage method.