Optimize MediaType parsing

Prior to this commit, `MediaType.parseMediaType` would already rely on
the internal LRU cache in `MimeTypeUtils` for better performance. With
that optimization, the parsing of raw media types is skipped for cached
elements.
But still, `MediaType.parseMediaType` would first get a cached
`MimeType` instance from that cache and then instantiate a
`new MediaType(type, subtype, parameters)`. This constructor not only
replays the `MimeType` checks on type/subtyme tokens and parameters, but
it also performs `MediaType`-specific checks on parameters.
Such checks are not required, as we're using an existing `MimeType`
instance in the first place.

This commit adds a new protected copy constructor (skipping checks) in
`MimeType` and uses it in `MediaType.parseMediaType` as a result.

This yields interesting performance improvements, with +400% throughput
and -40% allocation/call in benchmarks. This commit also introduces a
new JMH benchmark for future optimization work.

Closes gh-24769

spring-core/src/main/java/org/springframework/util/MimeType.java

@@ -190,6 +190,18 @@ public class MimeType implements Comparable<MimeType>, Serializable {
 		}
 	}
 
+	/**
+	 * Copy-constructor that copies the type, subtype and parameters of the given {@code MimeType},
+	 * skipping checks performed in other constructors.
+	 * @param other the other MimeType
+	 */
+	protected MimeType(MimeType other) {
+		this.type = other.type;
+		this.subtype = other.subtype;
+		this.parameters = other.parameters;
+		this.toStringValue = other.toStringValue;
+	}
+
 	/**
 	 * Checks the given token string for illegal characters, as defined in RFC 2616,
 	 * section 2.2.
@@ -197,7 +209,7 @@ public class MimeType implements Comparable<MimeType>, Serializable {
 	 * @see <a href="https://tools.ietf.org/html/rfc2616#section-2.2">HTTP 1.1, section 2.2</a>
 	 */
 	private void checkToken(String token) {
-		for (int i = 0; i < token.length(); i++ ) {
+		for (int i = 0; i < token.length(); i++) {
 			char ch = token.charAt(i);
 			if (!TOKEN.get(ch)) {
 				throw new IllegalArgumentException("Invalid token character '" + ch + "' in token \"" + token + "\"");