Anim: Add 12, 8, and 6 FPS presets

Add 12, 8, and 6 FPS presets often used in stylized animation,
especially in 2D/Grease Pencil animation.

12 FPS to animate on 2's, 8 FPS on 3's, 6 FPS on 4's or for
early blocking stages or storyboard.

Pull Request: https://projects.blender.org/blender/blender/pulls/135712

scripts/presets/framerate/12.py

@@ -0,0 +1,3 @@
+import bpy
+bpy.context.scene.render.fps = 12
+bpy.context.scene.render.fps_base = 1

scripts/presets/framerate/6.py

@@ -0,0 +1,3 @@
+import bpy
+bpy.context.scene.render.fps = 6
+bpy.context.scene.render.fps_base = 1

scripts/presets/framerate/8.py

@@ -0,0 +1,3 @@
+import bpy
+bpy.context.scene.render.fps = 8
+bpy.context.scene.render.fps_base = 1

scripts/startup/bl_ui/properties_output.py

@@ -71,7 +71,7 @@ class RENDER_PT_format(RenderOutputButtonsPanel, Panel):
             fps_rate = round(fps / fps_base, 2)
 
         # TODO: Change the following to iterate over existing presets
-        custom_framerate = (fps_rate not in {23.98, 24, 25, 29.97, 30, 50, 59.94, 60, 120, 240})
+        custom_framerate = (fps_rate not in {6, 8, 12, 23.98, 24, 25, 29.97, 30, 50, 59.94, 60, 120, 240})
 
         if custom_framerate is True:
             fps_label_text = iface_("Custom ({:.4g} fps)").format(fps_rate)