pw_display: Facade backend implementations and demo

- pw_display
  - pw_display_null
  - pw_display_host_imgui
  - pw_display_pico_ili9341
  - pw_display_stm32f429i_disc1_stm32cube_ili9341
  - pw_display_teensy_ili9341
- pw_touchscreen
  - pw_touchscreen_null
  - pw_touchscreen_teensy_xpt2046
  - pw_touchscreen_teensy_stmpe610

Change-Id: I898efd067ad1b424a5789033091c2267216d8e19
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/70224
Commit-Queue: Anthony DiGirolamo <tonymd@google.com>
Reviewed-by: Armando Montanez <amontanez@google.com>
30 files changed