feat(desktop): log the keyboard map on startup

[nborodikhin]

Description

On the dev-oriented desktop build keyboard key are mapped to the device buttons, but the mapping is not very clear.

This PR prints out key mapping every time an binary invoked PAD_init() to remind developer of the mapping.

Change

• platform.c: add logKeyMap(), call it from PLAT_initInput()
• platform.h: CODE_* constants now use human-readable SDL_SCANCODE_* constants

Testing

• desktop build: the key map is in the log on startup:

[INFO] Keyboard map:
[INFO]   UP     Up
[INFO]   DOWN   Down
[INFO]   LEFT   Left
[INFO]   RIGHT  Right
[INFO]   SELECT `
[INFO]   START  Return
[INFO]   A      S
[INFO]   B      A
[INFO]   X      W
[INFO]   Y      Q
[INFO]   L1     Tab
[INFO]   R1     B
[INFO]   MENU   Space
[INFO]   POWER  Backspace