Restore lazy evaluation of project/build/finalName

This commit restores the read-only `finalName` so that its value can
be lazily resolved against `${project.build.finalName}`.

While doing the evaluation ourselves and not relying on a dedicated
field at all would have been better, the evaluation increased the
number of required dependencies for no good reason.

IDEs should not offer auto-completion for that read-only field and it
is not published in the generated site either.

Closes gh-16456

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/RepackageMojo.java

@@ -266,8 +266,7 @@ private File getTargetFile() {
 		if (!this.outputDirectory.exists()) {
 			this.outputDirectory.mkdirs();
 		}
-		String finalName = this.project.getBuild().getFinalName();
-		return new File(this.outputDirectory, finalName + classifier + "."
+		return new File(this.outputDirectory, this.finalName + classifier + "."
 				+ this.project.getArtifact().getArtifactHandler().getExtension());
 	}