FR: Add UnifontEX as last-resort fallback font (for when Noto doesn't have something)

[stgiga]

I've done some fiddling around with KOReader on my Kindle Touch, and I went to great effort to make the Lua files use UnifontEX instead of Noto, for the purposes of greater character support (the Noto used in KOReader seems to be taking it easy in how much Noto is used). After this (I don't know if the update would break this, I did this in March), I was even able to browse Wikipedia's Biangbiang Noodles article in KOReader (because UnifontEX has Unicode 15.1 support, including emoji and the infamous Biang and Taito Hanzi). Also, the Kindle displays it fine without needing to edit any size values.

Basically, I'm wanting to make KOReader support UnifontEX officially as a last-resort fallback font for stuff Noto can't display, and maybe the ability to make KOReader display everything in it, in case you have anything with emoji filenames from AO3.

Regular Unifont does have some limitations that UnifontEX doesn't have, such as needing two files to do Plane0+Plane1, something Emoji, "Aesthetic Text" (you'll find THIS on AO3 stories, which ironically the native Kindle hates), Unicode's internal Wingdings+Webdings family needs, as well as other stuff.

UnifontEX on KOReader works quite well. It does take some fiddling with the Lua files, but it DOES work. I haven't touched this since March, except today I finished the override, and I'm unsure if this will break, so I haven't updated. I'm using an original Kindle Touch for this.

[NiLuJe]

For clarity's sake, define "fiddling with the Lua files" (i.e., post the actual diff).

But, to be clear, given the size of Unifont: extremely unlikely.

If the code needs more massaging in order to add a fallback, sure, that's useful, but we can't really afford to ship 13MB of extra font ;).

[stgiga]

It does compress well, but I see your point.