Keymaps: left click select keymap changes

Both the active tools and selection are now on LMB, which leads to
various conflicts.

For that reason the LMB keymap now has a couple of differences
compared to before. These changes do not affect the RMB keymap.

* Context Menu: W -> RMB
* Select Tool activate: None -> W
* Set Cursor: RMB -> Shift+RMB
* Loop Select: Alt+LMB -> double click LMB
* Mask Feather Vertex Slide: Shift+RMB -> Ctrl+Shift+RMB
* Node Select: only with LMB now, no RMB

The idea behind the W key Select Tool shortcut is that various
tools can't be combined with selection, unlike the RMB keymap.
So this works as a quick shortcut to drop a tool
and go back to selection.

Tools: set Select Box tool as default, rather than Cursor.

This goes along with coming LMB select keymap changes,
where we want the user to be able to LMB click to select by default,
rather than set the cursor.
The cursor will still be directly setabble with shift+RMB.

release/scripts/startup/bl_ui/space_toolsystem_common.py

@@ -735,12 +735,12 @@ def keymap_from_context(context, space_type):
     use_simple_keymap = False
 
     # Press the toolbar popup key again to set the default tool,
-    # this is useful because the cursor tool is useful as a way
+    # this is useful because the select box tool is useful as a way
     # to 'drop' currently active tools (it's basically a 'none' tool).
     # so this allows us to quickly go back to a state that allows
     # a shortcut based workflow (before the tool system was added).
     use_tap_reset = True
-    # TODO: support other tools for modes which don't use the cursor.
+    # TODO: support other tools for modes which don't use select box.
     tap_reset_tool = "Cursor"
     # Check the tool is available in the current context.
     if ToolSelectPanelHelper._tool_get_by_name(context, space_type, tap_reset_tool)[1] is None: