Update layout docs, resolve some bugs

java/assets/layouts/LayoutSpec.md

java/assets/layouts/README.md

...o/inputmethod/latin/uix/settings/pages/DevLayoutEditor.kt

...rg/futo/inputmethod/latin/uix/settings/pages/Languages.kt

java/src/org/futo/inputmethod/latin/xlm/LanguageModel.kt

...rg/futo/inputmethod/latin/xlm/LanguageModelFacilitator.kt

java/src/org/futo/inputmethod/latin/xlm/ModelPaths.kt

java/src/org/futo/inputmethod/v2keyboard/BaseKey.kt

java/src/org/futo/inputmethod/v2keyboard/Keyboard.kt

java/src/org/futo/inputmethod/v2keyboard/MoreKeysBuilder.kt

lint.xml