[rcore] [SDL2] Fix maximizing, minimizing and restoring windows

[asdqwe]

Fixes RestoreWindow() (ref) for PLATFORM_DESKTOP_SDL that was using the incorrect call.

Fixes manually minimizing, maximizing and restoring the window not setting the correct FLAG_WINDOW_MAXIMIZED and FLAG_WINDOW_MINIMIZED respectively on PLATFORM_DESKTOP_SDL, and IsWindowMinimized() (ref) and IsWindowMaximized() (ref) that were INOP on PLATFORM_DESKTOP_SDL because the platform was missing event handling for SDL_WINDOWEVENT_MINIMIZED, SDL_WINDOWEVENT_MAXIMIZED and SDL_WINDOWEVENT_RESTORED (ref, ref). Manual detection to check if the window was maximized was necessary due to SDL2 restore being unreliable on some platforms (ref).

This PR was tested with SDL2.30.10 on Linux Mind 22.0. SDL3 wasn't tested but left placeholders for it and probably should work if SDL_WINDOW_MAXIMIZED was fixed there.

The PR can be tested with:

#include "raylib.h"
int main(void) {

    SetWindowState(FLAG_WINDOW_RESIZABLE);

    InitWindow(800, 450, "test");
    SetTargetFPS(60);

    while (!WindowShouldClose()) {

        if (IsKeyPressed(KEY_ONE)) MinimizeWindow();
        if (IsKeyPressed(KEY_TWO)) MaximizeWindow();
        if (IsKeyPressed(KEY_THREE)) RestoreWindow();
        TraceLog(LOG_INFO, "Minimized %i.  Maximized %i.", IsWindowMinimized(), IsWindowMaximized());

        BeginDrawing();
        ClearBackground(RAYWHITE);
        DrawText( "[1] Minimize\n[2] Maximize\n[3] Restore", 20, 20, 20, BLACK);
        EndDrawing();
     }
    CloseWindow();
    return 0;
}

[raysan5]

@asdqwe thanks for the improvements!