Revisit fix for gh-26905 in UriComponentsBuilder

This commit revisits the recently updated `PORT_PATTERN` in
`UriComponentsBuilder`. The fix introduced in gh-26905 fails with
ambiguous URL patterns, especially when the port and path parts of the
pattern are hard to differentiate, for example
"https://localhost:{port}{path}".

This commit reinstates the previous behavior without undoing the actual
fix. The only limitation introduced here is the fact that only a single
pattern variable is allowed for the port pattern part.

Fixes gh-27039

spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java

@@ -1297,4 +1297,14 @@ class UriComponentsBuilderTests {
 				.isInstanceOf(NumberFormatException.class);
 	}
 
+	@Test // gh-27039
+	void expandPortAndPathWithoutSeparator() {
+		URI uri = UriComponentsBuilder
+				.fromUriString("ws://localhost:{port}{path}")
+				.buildAndExpand(7777, "/test")
+				.toUri();
+		assertThat(uri.toString()).isEqualTo("ws://localhost:7777/test");
+	}
+
+
 }