Rename some `MergedAnnotation` methods to prevent using parent/child
terminology, specifically:

	`getDepth()` has been renamed `getDistance()`
	`getParent()` has been renamed `getMetaSource()`
	`getTypeHierarchy()` has been renamed `getMetaTypes()`

The parent child naming was particularly confusing given that the
parent/child relationships were inverted from the way that a lot of
users think about meta-annotations. For example, a `@RequestMapping`
having a parent of `@GetMapping` feels odd given that `@GetMapping`
is the thing declaring the meta-annotation relationship.

The new method names are designed to align more closely with existing
terms. For example, `getMetaSource` hints at the relationship with
`isMetaAnnotated` and `getSource`.

Closes gh-22946

Migrate all existing TestNG based assertions to AssertJ and add
Checkstyle rules to ensure they don't return.

See gh-23022

Closes gh-23014

Closes gh-23013

Revert 82d0e49d and instead create a `TransactionAssert` class.

Closes gh-23022

Migrate all existing JUnit Jupiter based assertions to AssertJ and add
Checkstyle rules to ensure they don't return.

See gh-23022

Prior to this commit, ScriptUtils did not properly split SQL
scripts that contained line endings for MS Windows.

Closes gh-23019

Closes gh-23020

Delete `TransactionTestUtils` and inline AssertJ assertions
instead.

Closes gh-23022

Migrate all existing JUnit 4 `assert...` based assertions to AssertJ
and add a checkstyle rule to ensure they don't return.

See gh-23022

Migrate all existing `assertThat(..., Matcher)` assertions to AssertJ
and add checkstyle rules to ensure they don't return.

See gh-23022

Closes gh-23015

Closes gh-22943

Closes gh-22943

Closes gh-22959

Closes gh-23006

This commit introduces a getOrEmpty(String) method in HttpHeaders that
returns an immutable, empty list if no values are present for the
specified header name. This is provided as a convenience over the
existing get(String) method which returns null in such cases.

Closes gh-22949