Use by-type semantics in bean overriding if no explicit name is provided

This change switches default behavior of `@TestBean`, `@MockitoBean` and
`@MockitoSpyBean` to match the bean definition / bean to override by
type in the case there is no explicit bean name provided via the
annotation. The previous behavior of using the annotated field's name
is still an option for implementors, but no longer the default.

Closes gh-32761

framework-docs/modules/ROOT/pages/testing/testcontext-framework/bean-overriding.adoc

@@ -58,10 +58,14 @@ by the corresponding `BeanOverrideStrategy`:
 [NOTE]
 ====
 In contrast to Spring's autowiring mechanism (for example, resolution of an `@Autowired`
-field), the bean overriding infrastructure in the TestContext framework does not perform
-any heuristics to locate a bean. Instead, the name of the bean to override must be
-explicitly provided to or computed by the `BeanOverrideProcessor`.
+field), the bean overriding infrastructure in the TestContext framework has limited
+heuristics it can perform to locate a bean. Either the `BeanOverrideProcessor` can compute
+the name of the bean to override, or it can be unambiguously selected given the type of
+the annotated field.
 
-Typically, the user provides the bean name via a custom annotation, or the
-`BeanOverrideProcessor` determines the bean name based on some convention.
+Typically, the user directly provides the bean name in the custom annotation in order to
+make things as explicit as possible. Alternatively, the bean is selected by type by the
+`BeanOverrideFactoryPostProcessor`.
+Some `BeanOverrideProcessor`s could also internally compute a bean name based on a
+convention or another advanced method.
 ====