Ensure parsing/tostring symmetry in ContentDisposition

Prior to this commit, building a "Content-Disposition" header to a
String and then parsing it back would not always result in the original
header.

This commit ensures that ContentDisposition guarantees this and honors
the "equals" contract.

Fixes gh-37064

spring-web/src/test/java/org/springframework/http/ContentDispositionTests.java

@@ -181,6 +181,15 @@ class ContentDispositionTests {
 			assertThat(cd.getFilename()).isEqualTo("foo\\bar \"baz\" qux \\\" quux.txt");
 		}
 
+		@Test
+		void parseBackslashInName() {
+			String s = "form-data; name=\"foo\\\"bar\"; filename=\"foo.txt\"";
+			ContentDisposition cd = ContentDisposition.parse(s);
+			assertThat(cd.getName()).isEqualTo("foo\"bar");
+			assertThat(cd.getFilename()).isEqualTo("foo.txt");
+			assertThat(cd.toString()).isEqualTo(s);
+		}
+
 		@Test
 		void parseBackslashInLastPosition() {
 			ContentDisposition cd = ContentDisposition.parse("form-data; name=\"foo\"; filename=\"bar\\\"");