library: vendors/kb_text_shape + vendors/file_utils; modules/ffi/stb_truetype.sx retired

kb_text_shape (v2.10, JimmyLefevre) had been LOST from the sx tree —
ffi/stb_truetype.sx referenced repo paths that no longer existed (and
nothing runs glyph_cache, so the dangling unit never fired). The
trimmed copy returns from the m3te project as a proper vendor:
curated c/kbts_api.h decls over the full upstream header, README with
provenance, and examples/1627 pinning context + font creation so the
unit compiles and runs in-suite. file_utils (in-house asset-read
helper with the Android AAssetManager hook) gets the same unit shape.

modules/ffi/stb_truetype.sx is gone: glyph_cache imports the three
vendored units (stb_truetype, kb_text_shape, file_utils) directly.

library/vendors/file_utils/README.md

@@ -0,0 +1,10 @@
+# vendors/file_utils — in-house asset-read helper
+
+Not third-party: a small in-house C helper kept under vendors/ because
+it ships as a `#import c` unit like the rest.
+
+- `read_file_bytes(path, *out_size)` — whole-file read, malloc'd bytes.
+- On Android, paths rooted inside the APK resolve through the
+  `AAssetManager` installed via `sx_android_set_asset_manager`
+  (modules/platform/android.sx calls it during activity startup; the
+  hook only exists in the `__ANDROID__` build of the unit).