Introduce ResourcePatternHint#toRegex

This change is done for several reasons:
 - Move the logic where it is documented.
 - Test it with ResourcePatternHintTests.
 - Allow RuntimeHintsPredicates to leverage this logic.

Closes gh-28620

spring-core/src/test/java/org/springframework/aot/hint/ResourcePatternHintTests.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.aot.hint;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ResourcePatternHint}.
+ *
+ * @author Sebastien Deleuze
+ */
+public class ResourcePatternHintTests {
+
+	@Test
+	void fileAtRoot() {
+		ResourcePatternHint hint = new ResourcePatternHint("file.properties", null);
+		assertThat(hint.toRegex().asMatchPredicate())
+				.accepts("file.properties")
+				.rejects("com/example/file.properties", "file.prop", "another-file.properties");
+	}
+
+	@Test
+	void fileInDirectory() {
+		ResourcePatternHint hint = new ResourcePatternHint("com/example/file.properties", null);
+		assertThat(hint.toRegex().asMatchPredicate())
+				.accepts("com/example/file.properties")
+				.rejects("file.properties", "com/file.properties", "com/example/another-file.properties");
+	}
+
+	@Test
+	void extension() {
+		ResourcePatternHint hint = new ResourcePatternHint("*.properties", null);
+		assertThat(hint.toRegex().asMatchPredicate())
+				.accepts("file.properties", "com/example/file.properties")
+				.rejects("file.prop", "com/example/file.prop");
+	}
+
+	@Test
+	void extensionInDirectoryAtAnyDepth() {
+		ResourcePatternHint hint = new ResourcePatternHint("com/example/*.properties", null);
+		assertThat(hint.toRegex().asMatchPredicate())
+				.accepts("com/example/file.properties", "com/example/another/file.properties")
+				.rejects("file.properties", "com/file.properties");
+	}
+
+	@Test
+	void anyFileInDirectoryAtAnyDepth() {
+		ResourcePatternHint hint = new ResourcePatternHint("com/example/*", null);
+		assertThat(hint.toRegex().asMatchPredicate())
+				.accepts("com/example/file.properties", "com/example/another/file.properties", "com/example/another")
+				.rejects("file.properties", "com/file.properties");
+	}
+}