Event System: remove tweak events in favor of click-drag

Supporting two kinds of dragging is redundant, remove tweak events as
they only supported 3 mouse buttons and added complexity from using the
'value' to store directions.

Support only click-drag events (KM_CLICK_DRAG) which can be used with
any keyboard or mouse button.

Details:

- A "direction" member has been added to keymap items and events which
  can be used when the event value is set to KM_CLICK_DRAG.

- Keymap items are version patched.

- Loading older key-maps are also updated.

- Currently the key-maps stored in ./release/scripts/presets/keyconfig/
  still reference tweak events & need updating. For now they are updated
  on load.

Note that in general this wont impact add-ons as modal operators don't
receive tweak events.

Reviewed By: brecht

Ref D14214

release/scripts/modules/rna_keymap_ui.py

@@ -180,6 +180,10 @@ def draw_kmi(display_keymaps, kc, km, kmi, layout, level):
                 subrow.prop(kmi, "type", text="")
                 subrow.prop(kmi, "value", text="")
 
+            if map_type in {'KEYBOARD', 'MOUSE'} and kmi.value == 'CLICK_DRAG':
+                subrow = sub.row()
+                subrow.prop(kmi, "direction")
+
             subrow = sub.row()
             subrow.scale_x = 0.75
             subrow.prop(kmi, "any", toggle=True)