Add pgvector support

[e253]

Adds necessary changes for electric-sql/pglite#95.

[pmp-p]

Thanks for the contribution ! Though it may not be necessary to use static loading anymore : we are currently working on loading shared extensions in pg 16.2. Keeping this open until shared vector has been tested and we will get back to you.

[AntonOfTheWoods]

@pmp-p , @samwillis , I guess that is the disadvantage of creating new non-public repos and working there... Community contributions that will likely never get used.

[pmp-p]

@AntonOfTheWoods that contribution is suitable for a wasi build and maybe later native retargeting. The problem is more pg not accepting github PR, adding wasm support + dlopen is unlikely to be a small patch to upstream in the mail :( . And same the other way around, though patchwork is ready it is not a format suitable for github contributions So we still have to think an efficient way that will fit both.

I think leaving open PR against a pg git fork are the way to go.