Move field injection logic to `BeanOverrideTestExecutionListener`

[sbrannen]

Overview

For bean override support (@MockitoBean, @TestBean, etc.), the logic for field injection currently resides in the BeanOverrideRegistry.

However, that field injection logic should ideally reside solely in BeanOverrideTestExecutionListener, and the BeanOverrideRegistry should serve a single role, namely the role of a registry.

Related Issues

• Provide first-class support for Bean Overrides with @ContextHierarchy #34723