feat(android): installable fonts

[mcdurdin]

Android does not currently support system-wide installable fonts. This limitation is painful for many of our users. It would be good to reach out to Android project and see if this is something that could be addressed.

Some (not comprehensive) references:

• https://community.software.sil.org/t/installing-charis-sil-on-android/7024
• https://community.software.sil.org/t/can-a-custom-font-be-installed-on-the-phone/3908
• https://community.software.sil.org/t/font-issue-with-easy-chakma-keyboard-on-android-8-1/2857/2
• https://community.software.sil.org/t/installing-keyman-package-on-android/4424/5
• https://community.software.sil.org/t/hebrew-vowel-position-different-on-ios-and-android/4356/4
• https://community.software.sil.org/t/keyman-conlang/4776
• https://github.com/keymanapp/keyman/issues/12457
• https://github.com/keymanapp/keyman/issues/12493 (was a dual ios/android issue)
• https://github.com/keymanapp/keyman/issues/2159