Fixes#6005.
If a key has no default behavior, and the expectation is to trigger the
key default, then set the output behavior to null, so that the caller
will do the action.
This fixes a regression in #5553, which handled the situation where a
rule was triggered but then default output was expected (common example
is final sigma transform only when a word is finished).
The regression resulted in suggestions rotating unexpectedly when
pressing a modifier key.
Fixes#6364.
Removes `&layerChanged` and adds `&newLayer` and `&oldLayer` system
stores with the additional nuances around values as described in #6364.
The Caps Lock change I made in the previous commit broke
desktop Caps Lock handling. The fix was a little more
convoluted. Turns out that _UpdateVKShift is also pretty
crufty. I simplified it, removing dead code.
Selecting the new Caps Lock `caps` layer was not correctly setting the
layer state in the key event to `caps`, which caused Caps Lock rules
to fail to match.
Relates to #5853 and others.
Selection management was not working properly with the various
OutputTargets:
1. When there is a non-empty selection, rules have no context -- it's
like new text.
2. Backspace over a selection deletes just the selection.
3. Typing a character replaces the selection, of course, and collapses
the caret to the end of the new text.
4. `hasSelection` is a very strange name for `OutputTarget` descendants.
It doesn't mean "has an active selection" but rather, kinda means
"supports selection internally".
5. Added `isSelectionEmpty` which is used for some of the new selection
rules above.
Note that the `touchAlias` OutputTarget class does not currently support
selection. I hope we can deprecate `touchAlias` with the use of
`inputMode` (#3030) in the future, rather than adding support for
selection.
Relates to #5853.
Two things happened here:
1. Construction of Mocks made an assumption that the selection should
always be deleted (outputTarget.ts:363). However, for NewContext and
PostKeystroke processes, we don't want to change anything.
2. Even if nothing is changed, the transcription would emit what is
in theory a no-op ruleTransform (insert="", deleteLeft=0,
deleteRight=0). But apps would treat this as deleting the selection.
This fix goes a little broader than I would have preferred, but adds a
readonly mode to the transcription and mock model, so that we can
control explicitly when changes are applied to the text store.
