1092573: Update keyboard-layouts.json to include lv in keyboard list

related to https://bugzilla.mozilla.org/show_bug.cgi?id=1092573
1092573: Update languages_all.json -> include Latvian (lv) in builds
Merge pull request #26378 from jm-gailis/master

1092573 - include Latvian (lv) in FxOS builds. r=stas