Fix path within mapping when pattern contains ".*"

Prior to this commit, extracting the path within handler mapping would
result in "" if the matching path element would be a Regex and contain
".*". This could cause issues with resource handling if the handler
mapping pattern was similar to `"/folder/file.*.extension"`.

This commit introduces a new `isLiteral()` method in the `PathElement`
abstract class that expresses whether the path element can be compared
as a String for path matching or if it requires a more elaborate
matching process.

Using this method for extracting the path within handler mapping avoids
relying on wildcard count or other properties.

Fixes gh-29712

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

@@ -118,6 +118,10 @@ class LiteralPathElement extends PathElement {
 		return this.text;
 	}
 
+	@Override
+	public boolean isLiteral() {
+		return true;
+	}
 
 	@Override
 	public String toString() {

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

@@ -25,6 +25,7 @@ import org.springframework.web.util.pattern.PathPattern.MatchingContext;
  * Common supertype for the Ast nodes created to represent a path pattern.
  *
  * @author Andy Clement
+ * @author Brian Clozel
  * @since 5.0
  */
 abstract class PathElement {
@@ -99,6 +100,14 @@ abstract class PathElement {
 		return 0;
 	}
 
+	/**
+	 * Return whether this PathElement can be strictly {@link String#compareTo(String) compared}
+	 * against another element for matching.
+	 */
+	public boolean isLiteral() {
+		return false;
+	}
+
 	/**
 	 * Return if the there are no more PathElements in the pattern.
 	 * @return {@code true} if the there are no more elements

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

@@ -304,7 +304,7 @@ public class PathPattern implements Comparable<PathPattern> {
 		// Find first path element that is not a separator or a literal (i.e. the first pattern based element)
 		PathElement elem = this.head;
 		while (elem != null) {
-			if (elem.getWildcardCount() != 0 || elem.getCaptureCount() != 0) {
+			if (!elem.isLiteral()) {
 				break;
 			}
 			elem = elem.next;

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

@@ -67,6 +67,10 @@ class SeparatorPathElement extends PathElement {
 		return new char[] {this.separator};
 	}
 
+	@Override
+	public boolean isLiteral() {
+		return true;
+	}
 
 	@Override
 	public String toString() {