Deprecate ReplaceTestFunctionPrefixWithAttributeRector

[TomasVotruba]

ReplaceTestFunctionPrefixWithAttributeRector is not a common upgrade path and is not part of any set. Users should only use sets, so a rule that is only reachable by manual registration is better implemented as a local custom rule.

Rule turns test-prefixed methods into #[Test] attributed ones:

 class SomeTest extends \PHPUnit\Framework\TestCase
 {
-    public function testOnePlusOneShouldBeTwo()
+    #[Test]
+    public function onePlusOneShouldBeTwo()
     {
         $this->assertSame(2, 1+1);
     }
 }

This is a project-specific naming preference, not an upgrade. Deprecated the same way as other deprecated rules here: DeprecatedInterface + refactor() throwing ShouldNotHappenException, tests removed.