Use ei_text in the type-text example

[glamberson]

The type-text example reverse-mapped each character to a keycode and shift level through an xkb keymap and replayed synthetic key presses. The ei_text interface (libei 1.6.0) takes a UTF-8 string directly, so this binds ei_text and sends the string in one text.utf8(...) call.

It also drops the keymap handling, the keymap state, and the now-unused xkbcommon dev-dependency. The seat reports when the server does not advertise ei_text instead of panicking.

Uses the generated ei::Text bindings from #12; independent of the high-level EiEvent/EisRequest work in #27.

[ids1024]

It would probably be good to have this as a separate example, or a command line argument on the same example. Although ei_text is definitely the correct way to do this now on compositors that support it, the current type-text example is a nice demonstration and test case for the ei_keyboard protocol.

[glamberson]

Sure. I've kept type-text unchanged and added the ei_text version as a separate type-text-ei example, so the ei_keyboard demonstration (and its xkbcommon dev-dep) stays. Rebased onto master; the PR is now purely additive.