Cleanup: ChangeParentPom recipe

[jevanlingen]

What's changed?

Nothing, just refactoring.

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[jevanlingen]

💡 This test contained the same code as the doesNotAddGlobalProperties test.

[jevanlingen]

💡 Contained nearly the same code as the AddPropertyVisitor.

[jevanlingen]

💡 The getValue does already take properties into account:

rewrite/rewrite-maven/src/main/java/org/openrewrite/maven/tree/ResolvedPom.java

Lines 284 to 289 in 5d38687

	public @Nullable String getValue(@Nullable String value) {
	if (value == null) {
	return null;
	}
	return placeholderHelper.replacePlaceholders(value, this::getProperty);
	}