Deprecate the following obsolete functions and properties:
* `keyman.helpURL`
* `keyman.util.rgba`
* `keyman.util.toFloat`
* `keyman.util.toNumber`
* `keyman.util.toNzString`
Use correct language for code blocks in Keyman Engine for Web
documentation.
Test-bot: skip
- `kmw` is no longer used on this page, so we don't have to mention it
- the `european2` keyboard is deprecated and the text mentions EuroLatin,
so changed the sample to `sil_euro_latin`
Note: build.sh updated to make sure that test:help build action:target
doesn't also call test.sh by adding `:_all` meta-target.
Note: CI will need a new help-keyman-com.sh build step to deploy web
engine help.
Fixes: #12347
