WM: Add utility wmOrtho2_*** funcs

Currently there are inconsistencies with pixel alignment.
but this commit has no functional changes.

- wmOrtho2_region_ui for UI/Text.
- wmOrtho2_region_pixelspace for 2D drawing.
- wmOrtho2_pixelspace - when the region isn't used.

source/blender/editors/interface/interface.c

@@ -1347,8 +1347,8 @@ void uiDrawBlock(const bContext *C, uiBlock *block)
 	glMatrixMode(GL_MODELVIEW);
 	glPushMatrix();
 	glLoadIdentity();
-	
-	wmOrtho2(-0.01f, ar->winx - 0.01f, -0.01f, ar->winy - 0.01f);
+
+	wmOrtho2_region_ui(ar);
 	
 	/* back */
 	if (block->flag & UI_BLOCK_RADIAL)