keymap: Add option `lockOnRelease` for LockGroup() It enables to use e.g. the combination `Control + Shift` *alone* to switch layouts, while keeping the use of `Control + Shift + other key` (typically for keyboard shortcuts). The specification of `LockGroup()` is changed to: - On key *press*: - If `lockOnRelease` is set, then key press has no effect. - Otherwise: - if the `group` is absolute, key press sets the *locked* keyboard group to `group`; - otherwise, key press adds `group` to the *locked* keyboard group. In either case, the resulting *locked* and *effective* group is brought back into range depending on the value of the `GroupsWrap` control for the keyboard. - On key *release*: - If `lockOnRelease` is not set, then key release has no effect. - Otherwise, if any other key was *pressed* after the locking key, then key release has no effect. - Otherwise, it has the same effect than a key press *without* `lockOnRelease` set. This is really useful for people coming from other platforms, such as Windows. It fixes a [20-year old issue] inherited from the X11 ecosystem, by extending the [XKB protocol key actions]. As it is incompatible with X11, this feature is available only using the keymap text format v2. [20-year old issue]: https://gitlab.freedesktop.org/xorg/xserver/-/issues/258 [XKB protocol key actions]: https://www.x.org/releases/current/doc/kbproto/xkbproto.html#Key_Actions