Documentation editor doesn't handle BigQuery structs

### Expected behavior

Assume we have a simple table:
```sql

SELECT id
, STRUCT(
field_one
, field_two
, field_three
) AS struct_one
, STRUCT(
field_one
, field_two
, field_three
) AS struct_two
FROM table_one

```

Documentation editor should show:
- id
- struct_one
- struct_one.field_one
- struct_one.field_two
- struct_one.field_three
- struct_two
- struct_two.field_one
- struct_two.field_two
- struct_two.field_three

### Actual behavior

Currently Documentation Editor shows:
- id
- struct_one
- struct_two

(so fields from the structs are not present)

Moreover if dbt YAML already contains docs on subfields, they are removed upon saving the docs in the Documentation Editor.

### Steps To Reproduce

Any table with BigQuery STRUCT.

### Log output/Screenshots

_No response_

### Operating System

Ubuntu 20.04.6 LTS (Focal Fossa)

### dbt version

1.6.9

### dbt Adapter

bigquery

### dbt Power User version

0.36

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!