Add PathPatternRegistry for handler mapping matching

Previously `HandlerMapping` implementation were heavily relying on
`String` path patterns, `PathMatcher` implementations and dedicated maps
for matching incoming request URL to an actual request handler.

This commit adds the `PathPatternRegistry` that holds `PathPattern`
instances and the associated request handler — matching results are then
shared as `PathMatchResult` instances. `AbstractUrlHandlerMapping` will
use this registry directly, but other components dealing with request
matching (like `PatternsRequestCondition`) will directly use ordered
`PathPattern` collections since ordering is important there.

This opens the door for faster request matching and simplifies the
design of this part.

Issue: SPR-15608

spring-web/src/main/java/org/springframework/web/util/pattern/PathPatternComparator.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2002-2017 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
+ *
+ *      http://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.web.util.pattern;
+
+import java.util.Comparator;
+
+/**
+ * {@link PathPattern} comparator that takes account of a specified
+ * path and sorts anything that exactly matches it to be first.
+ *
+ * <p>Patterns that have the same specificity are then compared
+ * using their String representation, in order to avoid
+ * considering them as "duplicates" when sorting them
+ * in {@link java.util.Set} collections.
+ *
+ * @author Brian Clozel
+ * @since 5.0
+ */
+public class PathPatternComparator implements Comparator<PathPattern> {
+
+	private final String path;
+
+	public PathPatternComparator(String path) {
+		this.path = path;
+	}
+
+	@Override
+	public int compare(PathPattern o1, PathPattern o2) {
+		// Nulls get sorted to the end
+		if (o1 == null) {
+			return (o2 == null ? 0 : +1);
+		}
+		else if (o2 == null) {
+			return -1;
+		}
+		// exact matches get sorted first
+		if (o1.getPatternString().equals(path)) {
+			return (o2.getPatternString().equals(path)) ? 0 : -1;
+		}
+		else if (o2.getPatternString().equals(path)) {
+			return +1;
+		}
+		// compare pattern specificity
+		int result = o1.compareTo(o2);
+		// if equal specificity, sort using pattern string
+		if (result == 0) {
+			return o1.getPatternString().compareTo(o2.getPatternString());
+		}
+		return result;
+	}
+
+}