feat(tiny_ttf): backport Tiny TTF to lvgl 8 (#4727)

docs/libs/index.md

@@ -12,6 +12,7 @@
    png
    gif
    freetype
+   tiny_ttf
    qrcode
    rlottie
    ffmpeg

docs/libs/tiny_ttf.md

@@ -0,0 +1,35 @@
+# Tiny TTF font engine
+
+## Usage
+
+Use https://github.com/nothings/stb to render TrueType fonts in LVGL.
+
+When enabled in `lv_conf.h` with `LV_USE_TINY_TTF`
+`lv_tiny_ttf_create_data(data, data_size, font_size)` can be used to
+create a TTF font instance at the specified font size. You can then
+use that font anywhere `lv_font_t` is accepted.
+
+By default, the TTF or OTF file must be embedded as an array, either in
+a header, or loaded into RAM in order to function.
+
+However, if `LV_TINY_TTF_FILE_SUPPORT` is enabled,
+`lv_tiny_ttf_create_file(path, font_size)` will also be available,
+allowing tiny_ttf to stream from a file. The file must remain open the
+entire time the font is being used, and streaming on demand may be
+considerably slower.
+
+After a font is created, you can change the font size in pixels by using
+`lv_tiny_ttf_set_size(font, font_size)`.
+
+By default, a font will use up to 4KB of cache to speed up rendering
+glyphs. This maximum can be changed by using
+`lv_tiny_ttf_create_data_ex(data, data_size, font_size, cache_size)`
+or `lv_tiny_ttf_create_file_ex(path, font_size, cache_size)` (when
+available). The cache size is indicated in bytes.
+
+## API
+
+```eval_rst
+.. doxygenfile:: lv_tiny_ttf.h
+  :project: lvgl
+```