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/c/file_utils.h

@@ -0,0 +1,13 @@
+#ifndef FILE_UTILS_H
+#define FILE_UTILS_H
+
+unsigned char* read_file_bytes(const char* path, int* out_size);
+
+#ifdef __ANDROID__
+// Install the AAssetManager that `read_file_bytes` consults for paths
+// rooted inside the APK. Caller is responsible for passing the manager
+// from `ANativeActivity->assetManager` before any read_file_bytes call.
+void sx_android_set_asset_manager(void* m);
+#endif
+
+#endif