spanner: spansql.ParseDDL support for ARRAY<FLOAT32>

[ajroetker]

Client

Spanner

Expected vs actual behavior

We use the GoLang Spanner client to manage migrations of our Spanner DDL.
Spanner supports ARRAY for Vector Search which is half the byte cost of ARRAY.
We'd like to use a FLOAT32 but https://github.com/googleapis/google-cloud-go/blob/main/spanner/spansql/parser.go#L3202 does not support parsing ARRAY as valid DDL.

Additional context

Easy test, this works on spanner but not with spansql.ParseDDL

CREATE TABLE vectorTest (
  id STRING(MAX),
  vector ARRAY<FLOAT32>,
)
PRIMARY KEY (id);