Add Protocols for mapping inside dictionary view objects

[Gatsik]

Resolves #14555

[srittau]

The primer output is promising. Just one note about the protocols below.

[srittau]

Could you move these up to the other Supports* protocols?

Also, in typeshed (or at least in the _typeshed module) we have a slight preference for spelling out the methods supported in protocol, instead of deriving from other protocols, see for example SupportsItemAccess above. This makes it slightly easier for users to understand what methods are needed to fulfill a protocol instead of traversing through the class hierarchy.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

zope.interface (https://github.com/zopefoundation/zope.interface)
- src/zope/interface/common/collections.py:233: error: Incompatible types in assignment (expression has type "type[ItemsView[_KT_co, _VT_co]]", base class "ISet" defined the type as "type[AbstractSet[_T_co]]")  [assignment]
+ src/zope/interface/common/collections.py:233: error: Incompatible types in assignment (expression has type "type[ItemsView[_KT_co, _VT_co]]", base class "IMappingView" defined the type as "type[MappingView]")  [assignment]
- src/zope/interface/common/collections.py:237: error: Incompatible types in assignment (expression has type "type[KeysView[_KT_co]]", base class "ISet" defined the type as "type[AbstractSet[_T_co]]")  [assignment]
+ src/zope/interface/common/collections.py:237: error: Incompatible types in assignment (expression has type "type[KeysView[_KT_co]]", base class "IMappingView" defined the type as "type[MappingView]")  [assignment]
+ src/zope/interface/common/collections.py:241: error: Incompatible types in assignment (expression has type "type[ValuesView[_VT_co]]", base class "IMappingView" defined the type as "type[MappingView]")  [assignment]

static-frame (https://github.com/static-frame/static-frame)
+ static_frame/core/series_mapping.py:21: error: Unused "type: ignore" comment  [unused-ignore]
+ static_frame/core/series_mapping.py:26: error: Unused "type: ignore" comment  [unused-ignore]
+ static_frame/core/series_mapping.py:32: error: Unused "type: ignore" comment  [unused-ignore]

ibis (https://github.com/ibis-project/ibis)
- ibis/common/collections.py:140: error: Argument 1 to "KeysView" has incompatible type "ibis.common.collections.Mapping[K, V]"; expected "typing.Mapping[K, Any]"  [arg-type]
- ibis/common/collections.py:143: error: Argument 1 to "ItemsView" has incompatible type "ibis.common.collections.Mapping[K, V]"; expected "typing.Mapping[K, V]"  [arg-type]

discord.py (https://github.com/Rapptz/discord.py)
- discord/ext/commands/hybrid.py:508: error: Overlap between argument names and ** TypedDict items: "name", "description"  [misc]
+ discord/ext/commands/hybrid.py:508: error: Overlap between argument names and ** TypedDict items: "description", "name"  [misc]
- discord/ext/commands/hybrid.py:629: error: Overlap between argument names and ** TypedDict items: "name", "description"  [misc]
+ discord/ext/commands/hybrid.py:629: error: Overlap between argument names and ** TypedDict items: "description", "name"  [misc]

[srittau]

Thanks!