Fixes#7005.
If a developer used single digit values in stores, unquoted (which is
not really the usual approach, but should work just fine for non-zero
values), the KMW compiler would emit invalid single-digit hexadecimal
escapes for them, e.g. `"\x1"` instead of `"\x01"`.
Sample code:
```
store(option) 1
if(option = 1) + 'a' > 'one'
if(option = 2) + 'a' > 'two'
+ '1' > set(option = 1)
+ '2' > set(option = 2)
```
It is not immediately obvious from this code, but the value `1` is
actually a character with value `'\x01'` or `U+0001`!
The more usual approach will not encounter this problem:
```
store(option) '1'
if(option = '1') + 'a' > 'one'
if(option = '2') + 'a' > 'two'
+ '1' > set(option = '1')
+ '2' > set(option = '2')
```
Note that the following is a compile error (due to internal use of
null terminated strings).
```
store(option) 0
```
Fixes#7216.
The warning message 0x209A 'The rule will never be matched because its
key code is never fired.' was being generated multiple times for a
single line because the `JavaScript_Key` function it is generated by is
used for various purposes.
This PR keeps a cache of reported key rules to ensure that the message
is reported only once for a given key rule, and also improves the
reporting to clarify which specific key is unreachable, which makes it
easier to diagnose when using `any(k)` style messages, for example:
```
lao_phonetic.kmn (237): Warning: 209A The rule will never be matched for key 'ñ' because its key code is never fired.
```
This also reduces the warning to a hint, as this should not be a
blocking issue for a keyboard, rather just a place the keyboard author
can tidy up.
Picked up while reviewing code for conversion to C++. The compiler
could, in some circumstances emit garbage code for readonly groups
because we weren't testing all scenarios correctly. In practice, this
would have been rare as readonly groups don't emit characters, but it
should be fixed!
Fixes#6799.
For KeymanWeb compiled keyboards, readonly groups should never emit any
output. Rules in these groups permitted only to:
* `use` other readonly groups
* `call` external functions (which MUST NOT emit output)
* `set`, `reset` or `save` store values
The base kmx compiler does emit output for rules in readonly groups.
Thus, the KeymanWeb compiler, when it transpiles from the generated
.kmx, needs to omit output for any readonly group, while avoiding any
other potential change in behaviour.
