Fixes#5091.
If the user has a default language that is not a minimal BCP47 tag, such
as `zh-Hans-CN` vs `zh-CN`, or if the default language does not have a
mapping in our `TLanguageCodeUtils.TranslateWindowsLanguagesToBCP47`
function, then kmshell would crash on install of a keyboard that had no
language metadata specified (i.e. neither legacy metadata in .kmx nor
modern metadata in .kmp).
This crash arose because the elevated instance of kmshell would install
a local-machine reference to `zh-CN` (as it back-translated from a
LangID), but the current user install would look for `zh-Hans-CN`, read
from the Windows registry `HKCU\Control Panel\International\User Profile`.
To further complicate matters, it is possible for the current user to
have a different default language than the elevated user on the machine.
Keyman was assuming that the default language was the same in both
cases.
This fix passes in the current user's default BCP47 and LangID to the
elevated portion of the keyboard install, so we can guarantee that
keyboard install which needs to use the default language, actually
installs for the current user's actual language code, and not a
canonicalized version (or a totally different code in the case of
elevation to an alternate admin user account).
