[botoddly]

For stanoddly/Pixely#709.

Change

• XDL_VERSION is 3.4.20-11. That brings XDL_SetWindowInputRegion from 3.4.20-10 (Add XDL_SetWindowInputRegion, which lets mouse input through a window outside given rectangles XDL#28) into XDL.g.cs, in its own commit.
• generator.json binds SDL3_ttf/XDL_ttf.h, which 3.4.20-11 adds (Add letter spacing, OpenType features and variation axes to SDL_ttf XDL#29). XDL_ttf.g.cs holds XDL_SetFontCharSpacing, XDL_SetFontFeatures and XDL_SetFontVariations, loaded from XDL3_ttf like the rest of SDL_ttf. tests/native/xdlsharp_layout.c includes the header.

Tested locally

• The bindings were generated from the 3.4.20-11 release headers, and --check passes with the local clang.
• XdlSharp.Tests: 15 passed.
• Before the XDL release, Pixely's font tests passed against a local pack of this branch whose linux-x64 native package carried the patched libXDL3_ttf.so.