Handle MIME type parameter names case-insensitively

MIME type parameter names are case-insensitive, and MimeType already
stores them in a LinkedCaseInsensitiveMap. Several code paths, however,
still compared them with case-sensitive String.equals().

As a result, MimeType.hashCode() disagreed with MimeType.equals() for
parameter names that differ only in case, breaking the equals/hashCode
contract: text/plain;FOO=bar and text/plain;foo=bar are equal but hash
differently, so one is not found in a hash-based collection holding the
other. MimeType.compareTo() had the same blind spot for the charset
parameter.

MediaType was affected in two further ways: an out-of-range quality
value escaped validation when spelled Q=, and removeQualityValue() left
a Q= parameter in place.

Signed-off-by: Artyom Tsvirko <36863599+lArtiquel@users.noreply.github.com>

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

@@ -135,6 +135,12 @@ class MediaTypeTests {
 				MediaType.parseMediaType("audio/basic;q=1.1"));
 	}
 
+	@Test
+	void parseMediaTypeIllegalQualityFactorWithUpperCaseParameterName() {
+		assertThatExceptionOfType(InvalidMediaTypeException.class).isThrownBy(() ->
+				MediaType.parseMediaType("audio/basic;Q=1.1"));
+	}
+
 	@Test
 	void parseMediaTypeIllegalCharset() {
 		assertThatExceptionOfType(InvalidMediaTypeException.class).isThrownBy(() ->
@@ -293,6 +299,18 @@ class MediaTypeTests {
 		assertThat(new MediaType("text", "*").isConcrete()).as("text/* concrete").isFalse();
 	}
 
+	@Test
+	void removeQualityValue() {
+		assertThat(MediaType.parseMediaType("audio/basic;q=0.8").removeQualityValue())
+				.isEqualTo(MediaType.parseMediaType("audio/basic"));
+	}
+
+	@Test
+	void removeQualityValueWithUpperCaseParameterName() {
+		assertThat(MediaType.parseMediaType("audio/basic;Q=0.8").removeQualityValue())
+				.isEqualTo(MediaType.parseMediaType("audio/basic"));
+	}
+
 	@Test  // gh-26127
 	void serialize() throws Exception {
 		MediaType original = new MediaType("text", "plain", StandardCharsets.UTF_8);