Add completion types for completions obtained with matchers

[krassowski]

Fixes #12820 by adding a property-setting decorator to matcher functions which allows to pass additional metadata about matches returned by the matcher functions. I kept the changes to minimum to maintain full backward-compatibility, and I refrained from refactoring to NamedTuples being wary of potential performance penalty.

Regarding implementation as in this PR

General questions:

• should the matcher decorators be exposed as public API? The matchers are already exposed publicly via IPCompleter.custom_matchers, so it might be useful to someone, but since custom_matchers is not documented anywhere I don't think this is a must
• what should the type for dictionary key be named?
• should there be a separate type for %config and %colors completions, or should both be mapped to param?

For context:

• jedi types: module, class, instance, function, param, path, keyword, property and statement
• LSP completion kinds: Text, Method, Function, Constructor, Field, Variable, Class, Interface, Module, Property, Unit, Value, Enum, Keyword, Snippet, Color, File, Reference, Folder, EnumMember, Constant, Struct, Event, Operator, TypeParameter

Notes:

• there is a way to add typing annotations for matchers which would capture that these are callables with extra attributes but it requires Protocol, but is only available since Python 3.8 (or waiting until Declare and use attributes of function objects python/mypy#2087 gets addressed).

[krassowski]

Superseded by work in #13745.