Move the deprecated component-overrides.txt support to legacy

The META-INF/component-overrides.txt file and the ComponentAnnotationLoader#COMPONENT_OVERRIDE_LIST constant have been deprecated since 3.3M1 in favor of component priorities declared in META-INF/components.txt (e.g. 500:org.example.MyComponent).

This task moves them to the xwiki-commons-legacy-component-default module:

• COMPONENT_OVERRIDE_LIST is removed from ComponentAnnotationLoader in xwiki-commons-component-default and re-added through an aspect in the legacy module.
• The support for META-INF/component-overrides.txt (components declared there being registered with the highest priority of 0) is only provided when the legacy module is installed, which is the case in XWiki Standard.

Impact for extension developers

Extensions still using a META-INF/component-overrides.txt file keep working in XWiki Standard, but should declare a priority in META-INF/components.txt instead. Code running without the legacy modules will not see COMPONENT_OVERRIDE_LIST anymore and will ignore component-overrides.txt files.