feat(key): Add KeyFormat

[Emilxyz]

This pull request adds a KeyFormat class to allow for easier creation of custom Keys using the API.

KeyFormat has following functionality:

• Configuring a fallback namespace to be used when no other namespace is specified in the key parsing
• Configuring a default separator to be used when parsing keys
• KeyFormat#parse(String) which parses a input string using the configured separator and fallback namespace
• KeyFormat#key(String) which creates a key using the configured namespace and the input string as value
• KeyFormat#parseable(String) to check if a input string can be parsed using the configuration of the key format
• KeyFormat#asString(Key) to turn a key into a String using the configuration
• KeyFormat#asMinimalString(Key) to turn a Key into its minimal String using the configuration

Closes #1222

[Emilxyz]

As for #1249, im unsure on what best to name that method, as we can't have another #key(String). I see 2 options and need some input on them:

A:
The method to parse an input string is renamed to #parse(String).
#key(String) takes in the value only and always uses the configured namespace.

B:
#key(String) remains the method for parsing.
And the method taking only a value is named something like #value(String).

I like A more, just cause it makes more sense to me and sounds better (at least in my head). But, we would be breaking consistency with Key#key(String), so I would also agree in going with B. When going with B we would need to come up with a better name for that method as I really don't like #value, but it's the best I could come up with rn.

I understand that the methods in Key were named to be used as static imports, but none of these methods are static and always require an instance of a key format. So, in my opinion, it might be better to disregard the consistency and go with what makes more sense/sounds nicer.

[Emilxyz]

Another thing I thought about recently, is that it might be better to move the actual logic of creating/checking parsability of keys into the key format class. All the overloads I added in Key could be removed then and the existing ones just forward into KeyFormat.minecraft().

[Emilxyz]

Went ahead and implemented option A now, can always just rename the methods again if required.

[imDaniX]

For consistency, we can use the name parseKey instead, create Key#parseKey, deprecate Key#key(String) and Key#key(String, char), and move their responsibility to newly created Key#parseKey. It'll also allow for creating Key#parseKey(String keyStr, String fallbackNamespace).

But ofc, I'm not a maintainer, just my thoughts on the topic.