Convert remaining template_preprocess functions

I think that is a real failure

The test fails because its expecting template_preprocess_layout to exist in $theme_definitions['test_layout_theme']['preprocess functions']. This doesn't exist because we use initial preprocess now instead. There is a snippet in \Drupal\Core\Theme\Registry::processExtension that is responsible here:

// Add template_preprocess_HOOK function, if no initial preprocess
// callback is defined.
if (empty($info['initial preprocess']) && function_exists('template_preprocess_' . $hook)) {
  // @todo trigger deprecation in https://www.drupal.org/project/drupal/issues/3513595.
  $info['preprocess functions'][] = 'template_preprocess_' . $hook;
}

I suspect we don't need testThemeProvidedLayout anymore, or we need something else to verify initial preprocess is set or invoked, specifically for layouts in themes.

I must have missed it in debugging, but initial preprocess is right there for us to inspect. Pushed a fix for this.

Looks right!

I did my normal check except the zebra check.

All deprecations are right
No double __
They all set __FUNCTION__

All initial preprocess are for the correct method.
All comments are correct.
I'll do the zebra check later before marking this.

Had a chance to do the zebra check looks good to me!
Between this and 9 I think we're good to go on this.

Committed/pushed to 11.x, thanks!