Need to improve the remote entity

[albaintor]

Hi,

following this PR and discussion in architecture, one need to discuss about what solution could be proposed and implemented to address these needs.
I understand that you don't want to make too complicated entities, including the existing media entity.
But on the other hand the remote entity is quite basic and could not be considered as a remote but as a "passthrough of custom commands". It holds no command, including the common commands that you have on all remotes

These missing commands (for multimedia remotes mostly but not only) could fill the following usages:

• Navigate into menus (arrow keys)
• Related commands : select, back, exit, info, context menu, main menu...
• Type in numbers (a chapter number, a media position, a TV channel)
• Type in a string (AppleTV raises text input when you select a text field)
• Select an item in a list : audio track, subtitles language, TV channel, a radio

All of this (except the extraction of lists of items selection such as audio tracks/subtitles) could be done through the send_command method of the remote entity, but the problem is that integrations have all different command names (Key.UP, UP, ARROW_UP for the same command) for the same function, so this is not possible to design a UI that would work for every devices. This is the reason why there is (many) different custom cards which have the same features but designed for a given device.
My initial PR was to define in a const file those command names that would be reused and mapped to the device commands by the integration. Maybe it should only be a matter of documentation, like "we all agree to use those command names and map them".

The other thing which is missing is the capability of the device : the send_command is not enough For example Nvidia shield tv and AppleTV offer a list of available applications that you mapped on sources on media_entity. Some devices have more capabilities such as returning the list of audio tracks, subtitles and the UI will need to have knowledge of these capabilities

Still I don't have any concrete solution beyond the PR that I posted. To summarize, the remote entity should get closer a real remote