PathPattern does not use custom separator

Prior to this commit, `PathPattern::extractPathWithinMapping`
would always use the default path pattern separator `/` when extracting
the path within the pattern of a matched route.

This commit ensures that `PathPattern` uses the configured separator
when extracting the path within the matched mapping.

Fixes gh-23168

Author: bclozel

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

@@ -339,7 +339,7 @@ public PathContainer extractPathWithinPattern(PathContainer path) {
 					}
 				}
 			}
-			resultPath = PathContainer.parsePath(buf.toString());
+			resultPath = PathContainer.parsePath(buf.toString(), String.valueOf(this.separator));
 		}
 		else if (startIndex >= endIndex) {
 			resultPath = PathContainer.parsePath("");

spring-web/src/test/java/org/springframework/web/util/pattern/PathPatternTests.java

@@ -707,6 +707,17 @@ public void extractPathWithinPattern() throws Exception {
 		checkExtractPathWithinPattern("/", "//", "");
 	}
 
+	@Test
+	public void extractPathWithinPatternCustomSeparator() {
+		PathPatternParser ppp = new PathPatternParser();
+		ppp.setSeparator('.');
+		PathPattern pp = ppp.parse("test.**");
+		PathContainer pathContainer = PathContainer.parsePath("test.projects..spring-framework", ".");
+		PathContainer result = pp.extractPathWithinPattern(pathContainer);
+		assertThat(result.value()).isEqualTo("projects.spring-framework");
+		assertThat(result.elements()).hasSize(3);
+	}
+
 	@Test
 	public void extractUriTemplateVariables_spr15264() {
 		PathPattern pp;