Support pgvector extension in codegen

[comfuture]

Describe the bug

edgedb python doesn't seems support pgvector yet.
When I try to create codegen for pgvector, it throws an error.

Reproduction

Simple edgeql that uses pgvector:

with
  vec as module ext::pgvector,
  target := <vec1536>$vector,
  threshold := <float64>$threshold

select Document {
  *,
  dist := vec::cosine_distance(target, .embedding)
}
filter .dist < threshold
order by .dist empty last
limit 5

Try to create code by edgedb-py command:

edgedb-py

Error message

$ edgedb-py
Found EdgeDB project: /workspace
Processing /workspace/queries/search_document.edgeql
Generating /workspace/queries/search_document_async_edgeql.py
Traceback (most recent call last):
  File "/home/vscode/.local/bin/edgedb-py", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/vscode/.local/lib/python3.11/site-packages/edgedb/codegen/cli.py", line 99, in main
    generator.Generator(args).run()
  File "/home/vscode/.local/lib/python3.11/site-packages/edgedb/codegen/generator.py", line 198, in run
    self._generate_files(suffix)
  File "/home/vscode/.local/lib/python3.11/site-packages/edgedb/codegen/generator.py", line 232, in _generate_files
    content = self._generate(name, query, dr)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.local/lib/python3.11/site-packages/edgedb/codegen/generator.py", line 319, in _generate
    out_type = self._generate_code(dr.output_type, name_hint)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.local/lib/python3.11/site-packages/edgedb/codegen/generator.py", line 452, in _generate_code
    el_code = self._generate_code_with_cardinality(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.local/lib/python3.11/site-packages/edgedb/codegen/generator.py", line 524, in _generate_code_with_cardinality
    rv = self._generate_code(type_, name_hint)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vscode/.local/lib/python3.11/site-packages/edgedb/codegen/generator.py", line 434, in _generate_code
    value = TYPE_MAPPING[base_type_name]
            ~~~~~~~~~~~~^^^^^^^^^^^^^^^^
KeyError: 'ext::pgvector::vector'

Expected behavior
Should be able to generate python file named search_document_async_edgeql.py

Versions (please complete the following information):

• OS: Linux 5ca54fafbd62 5.15.0-1040-azure #47-Ubuntu SMP Thu Jun 1 19:38:24 UTC 2023 x86_64 GNU/Linux
• EdgeDB version: 3.0+304325b
• EdgeDB CLI version: 3.3.0+071876c
• edgedb-python version: 1.5.0
• Python version: Python 3.11.4

Additional context
Add any other context about the problem here.

[comfuture]

Is this issue still being resolved? If it can't be resolved with codegen, I'll try to find another way.

[elprans]

@fantix, please merge #447 if it's ready

[fantix]

Yeah, it's ready now, I'll solve the issue in the failing test before merging (it might be a server bug due to recent changes in state management).