Handle MIME type parameter names case-insensitively

[lArtiquel]

MimeType keeps parameters in a LinkedCaseInsensitiveMap, so equals() matches names case-insensitively. parametersHashCode() hashes the raw key, so it doesn't — which breaks the equals/hashCode contract:

MimeType a = MimeType.valueOf("text/plain;FOO=bar");
MimeType b = MimeType.valueOf("text/plain;foo=bar");

a.equals(b);                            // true
a.hashCode() == b.hashCode();           // false
new HashSet<>(List.of(a)).contains(b);  // false

The charset branch in equals, hashCode and compareTo keys off PARAM_CHARSET.equals(key), so a parameter spelled Charset skips it and is compared as an opaque string, even though the constructor already resolved it through the same case-insensitive map:

MimeType.valueOf("text/plain;charset=UTF-8").equals(MimeType.valueOf("text/plain;charset=utf-8")); // true
MimeType.valueOf("text/plain;Charset=UTF-8").equals(MimeType.valueOf("text/plain;Charset=utf-8")); // false

MediaType has the same assumption in two more places: an out-of-range quality value escapes validation when spelled Q=1.1, and removeQualityValue() leaves a Q= parameter in place.

Fix is six lines — equalsIgnoreCase in the four comparisons, and a normalized key before hashing.

Two behavior changes, both bringing the uppercase spelling in line with the lowercase one: Charset=UTF-8 now equals Charset=utf-8, and Q=1.1 is now rejected at parse time. Four tests added, each failing before the change; spring-core, -web, -webmvc, -webflux, -messaging and -test suites pass.

[bclozel]

Duplicates #37008?

[lArtiquel]

No. #37008 rejects duplicate params within one header string; this is equals/hashCode across two instances. I applied it on main and the case is unchanged:

MimeType a = MimeType.valueOf("text/plain;FOO=bar");
MimeType b = MimeType.valueOf("text/plain;foo=bar");
a.equals(b);                   // true
a.hashCode() == b.hashCode();  // false

parametersAreEqual resolves the key through the LinkedCaseInsensitiveMap, parametersHashCode hashes it verbatim.

They only overlap in MimeTypeTests, so one needs a rebase. Can split the MediaType part out if you'd rather.