Add selected_options and unselected_options properties to ApplicationContext

[krittick]

Summary

Adds two new properties to ApplicationContext:

selected_options - Returns a dictionary containing the options and values that were selected by the user when the command was processed, if applicable.

unselected_options - Returns a list of Option objects (if any) that were not selected by the user when the command was processed.

These are mostly useful for handling things like command logging in on_application_command and such, and serves as an easier way to get the data than the user needing to do the parsing of actx.interaction.data themselves.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, typehinting, examples, ...)

[ChickenDevs]

LGTM