VideoBackends / VideoCommon: add support for specifying include files in shader code

Make the function name more explicit and a better match for
GetDisplayName.

Change NAME to CONFIG_NAME while I'm at it.

New rules:
`InsertNewlineAtEOF: true`
`RemoveSemicolon: true`
`RequiresClausePosition: WithPreceding`

My personal fork requires minimum iOS 14, so this is not required.