IME Composition Truncation + SDL_IsTextInputShown + SDL_ClearComposition (#5398)

* Fixes for IME Composition Truncation + Addition of SDL_ClearComposition, SDL_IsTextInputShown

* Fixed: Documentation and code style issues raised during code review.

src/dynapi/SDL_dynapi_overrides.h

@@ -857,3 +857,5 @@
 #define SDL_PremultiplyAlpha SDL_PremultiplyAlpha_REAL
 #define SDL_AndroidSendMessage SDL_AndroidSendMessage_REAL
 #define SDL_GetTouchName SDL_GetTouchName_REAL
+#define SDL_ClearComposition SDL_ClearComposition_REAL
+#define SDL_IsTextInputShown SDL_IsTextInputShown_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -928,3 +928,5 @@ SDL_DYNAPI_PROC(int,SDL_PremultiplyAlpha,(int a, int b, Uint32 c, const void *d,
 SDL_DYNAPI_PROC(int,SDL_AndroidSendMessage,(Uint32 a, int b),(a,b),return)
 #endif
 SDL_DYNAPI_PROC(const char*,SDL_GetTouchName,(int a),(a),return)
+SDL_DYNAPI_PROC(void,SDL_ClearComposition,(void),(),)
+SDL_DYNAPI_PROC(SDL_bool,SDL_IsTextInputShown,(void),(),return)