[Bf-funboard] Toggling proportional edit during transform

[David Jeske]

there are several different ways to add proportional edit during
transform.. here are a few of them..

(1) a quick hack that hardcodes the default "o" hotkey to toggle
proportional edit during transform, just like x/y/z toggles -- the problem
is, this will not match user-keybinds, and it just fixes this one request,
not this category of requests..

(2) add keybind contexts for each modal-operator -- cleaner, but compounds
an already compounding problem, that changing the keybind now requires
changing it in more places. it also requires a method to determine which
actions are viable during a modal operator, and exposing modal-operator
behavior toggles to keybinds

(3) allow keybinds to "flow up" out of modal operators into their
containing context, just like they flow out of editor-types into the
window-context. This means, much like the way g/s/r are usable during modal
operators to switch between those operators, any existing keybinds would
work (unless the modal operator over-rode those keybinds with local
behavior)... though some keybinds would cancel the modal operator. This
could be combined with (2)

and here is a consideration..

(a) currently during modal operators the header-controls are replaced with
modal-operator- status-text... this means the proportional edit toggle is
not visible. (1) could add proportional to modal-status-text, but this
seems an untenable pattern to continue for long. (2,3) suggest a pattern
which would move modal-status-text elsewhere, allowing the existing header
controls to be visible during modal-edit