[core] Fix mouse button order for PLATFORM_DESKTOP_SDL

[ghost]

Changes

• The SDL2 mouse button order is LEFT, MIDDLE, RIGHT, ... (doc), but raylib.h's MouseButton enum uses LEFT, RIGHT, MIDDLE, ... (L689-L690) like GLFW.
• Fixes the MOUSE_BUTTON_RIGHT and MOUSE_BUTTON_MIDDLE order by remapping them during the input polling for PLATFORM_DESKTOP_SDL (R1087-R1093, R1100-R1106).

Reference

• [core] Fix some mouse issues on SDL #3428 (comment)

Environment

• Tested on Linux (Ubuntu 22.04 64-bit) with SDL2 (2.28.4).

Edits

• 1: added line marks.
• 2: correction.

[raysan5]

@ubkp Oh! thanks for the review! I remember we talk about it and we left that review behind! thanks!