[3.0] Refactor dali key files

[3.0] Refactor dali key files

- Change type of dali key definition from extern const KEY
  to enum Key to remove unnecessary exported symbols.
- Seperate platform-specfic key mapping table (key-mapping-xxx.cpp)
  and common key functions (key-impl.cpp)
- Add Dali::Internal::Adaptor::KeyLookup::GetKeyName()
- Definition macros for key names are deprecated in utilX,
  so use key name string instead of macro in key-mapping-xxx.cpp.
- Apply some changed key names (XF86Back, XF86Home, XF86Menu)
- Remove old-named key variables - DALI_KEY_SEND, END, SELECT
- Add key code mapping entries for wayland

Change-Id: Ic1939e11f2c775880a50d674686e3b1de6413aec