include: Add winsqlite3.h.
Generated from https://sqlite.org/2025/sqlite-src-3510100.zip using
steps in Makefile.msc, with manual changes:
- SQLITE_CDECL, SQLITE_APICALL, SQLITE_CALLBACK and SQLITE_SYSAPI defines;
- remove wrong SQLITE_APICALL from varatgs sqlite3_str_appendf().