Add support for excluding ideographic characters from offline downloads

[ChrisLoer]

I just took a look at a ~200MB offline cache I collected for a narrow area around Beijing. It appeared to have ~24MB of tiles and ~161MB of font data. I suspect a large amount of that font data is CJK ideographs, which I don't need because I'm using the cache with an app that renders ideographs locally. We should add an option to OfflineDownload to exclude requests for glyph ranges that are part of i18n::allowsFixedWidthGlyphGeneration, expose the option in the various users of OfflineDownload (mbgl-offline, MGLOfflineStorage, ...?), and figure out how to document it appropriately.

/cc @kkaefer @tobrun @1ec5

[mb12]

@ChrisLoer Another approach to reduce the download bandwidth would be to download the .ttf file and generate the pbfs locally using node-fontnik. For 'Open Sans' fonts, this can reduce bandwidth by 6x (uncompressed).

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ChrisLoer]

Implemented in #13607.