[rcore][win32] Adding native win32 backend (#4869)

* win32 backend

* [rcore][win32] use SwapBuffers instead of wglSwapLayerBuffers

I don't understand OpenGL well enough to know the difference between
SwapBuffers and wglSwapLayerBuffers but the former seems to double
my FPS (from 2000 to about 4000 in core_vr_simulator).

* [rcore][win32] stop lying to the OS about when our window is updated

Instead of calling BeginPaint/EndPaint in WM_PAINT which signals to the
OS that our window content is updated, now when we encounter the WM_PAINT
message instead we return back to the raylib application which will
trigger it to render a new frame. We've replaced the call to BeginPaint
and EndPaint with a call to ValidateRect in SwapBuffers, which, means
we're now correctly telling the OS when our window content is actually
up-to-date.

Note that this doesn't fix the window content not being updated during
a window resize/move beacuse thos have their own message loop which
doesn't return early when it's time to paint.

* [rcore][win32] fallback to finding functions from opengl32.dll

* [rcore][win32] fixes from review/for gcc

* [rcore][win32] incorporate style conventions

* [rcore][win32] workaround unused function error SetupFramebuffer

* [rcore][win32] re-enable sanitize flags check for MSAA_4X

* [rcore][win32] more style changes and remove old DPI cases

Added some more missing spaces after conditional statements.  Also
made unsupported MSAA_4X an assert instead of an abort and also
removed dpi-aware cases for older OS's.  More changes would be needed
to support those OS versions, namely, removing the dependency
on shcore.

* [rcore][win32] fixes for compling with w64devkit without -DUNICODE

* Update build.zig

* Update build.zig

---------

Co-authored-by: Ray <[email protected]>

Author: marler8997

src/Makefile

@@ -342,6 +342,10 @@ ifeq ($(PLATFORM_OS), LINUX)
     CFLAGS += -fPIC
 endif
 
+ifeq ($(PLATFORM_OS),WINDOWS)
+    CFLAGS += -DUNICODE
+endif
+
 ifeq ($(RAYLIB_BUILD_MODE),DEBUG)
     CFLAGS += -g -D_DEBUG
 endif
@@ -628,6 +632,9 @@ ifeq ($(TARGET_PLATFORM),PLATFORM_DRM)
         LDLIBS += -latomic
     endif
 endif
+ifeq ($(TARGET_PLATFORM),PLATFORM_DESKTOP_WIN32)
+    LDLIBS = -lgdi32 -lwinmm -lopengl32 -lshcore
+endif
 ifeq ($(TARGET_PLATFORM),PLATFORM_ANDROID)
     LDLIBS = -llog -landroid -lEGL -lGLESv2 -lOpenSLES -lc -lm
 endif