Add PGlite version to a VFS file and report with `select version()`

There are a few things that would be useful here:

1. For the VFS to have a PGLITE_VERSION file containing the PGlite version number that *created* the database. This is useful to track which version of PGlite was used to run INITDB. It should probable not be updated when running the same datadir with a newer PGlite, it's purely a history of what version ran initdb (the PG_VERSION only contains the numeric major version of postgres that created the database and so we can't reuse this file)
2. Report the PGlite version when a user calls `SELECT VERSION()`

Postgres has it's version compiled into it via a `PG_VERSION` env var, which is used to construct `PG_VERSION_STR` here:

https://github.com/postgres/postgres/blob/53b2c921a0f9b56465ab65165c1909f9616ffa98/configure#L19226

Both are added to `confdefs.h` before compiling.

PGlite has a split compilation process, the WASM is built first, then the JS/TS wrapper and packaging. Our CI caches the WASM for faster builds. Ideally we use the existing changesets tooling to bump a version file somewhere that will trigger the rebuild of the WASM, and we patch the build config to something like:

```
cat >>confdefs.h <<_ACEOF
#define PG_VERSION_STR "PostgreSQL $PG_VERSION (PGlite $PGLITE_VERSION) on $host, compiled by $cc_string, `expr $ac_cv_sizeof_void_p \* 8`-bit"
_ACEOF
```

so that the resulting string is something like:

```
PostgreSQL 16.4 (PGlite v0.2.11) on x86_64-pc-linux-gnu, compiled by emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.68-git (20697f11b8f0fcb4c190acbf605e2361e39829ab), 32-bit
```

We should then modify our initdb to add the `PGLITE_VERSION' file - it should probably be the full output of `SELECT VERSION()` but maybe prefixed with `Created by: ` to make it apparent its the version stat created the database.

I would prefer all this to be baked into the WASM (or native build with libpglite) rather than in the JS/TS code.