More mouse and PIC fixes and the mouse now takes of the ration between guest resolution and actual render area size, multiplied by the DPI, when returning coordinate deltas, also unified the delta return function across the various emulated mice.

src/include/86box/plat.h

@@ -143,6 +143,7 @@ extern void     plat_vid_reload_options(void);
 extern uint32_t plat_language_code(char *langcode);
 extern void     plat_language_code_r(uint32_t lcid, char *outbuf, int len);
 extern void     plat_get_cpu_string(char *outbuf, uint8_t len);
+extern double   plat_get_dpi(void);
 
 /* Resource management. */
 extern void     set_language(uint32_t id);