sql.join() for building dynamic queries

postgres.js gives us parameterized tagged templates and the ability to nest sql partials, and this is fantastic, but I think it is missing a piece of the puzzle:

I want to be able concat partials together (that may contain query parameters), usually with some delimiter (eg whitespace, or a comma, or maybe an sql operator)

something like:

sql.join = (a: PendingQuery[] | Helper[], p: PendingQuery): PendingQuery {...}

would be amazing if this were a first-class feature in postgres.js

this should allow things like

let dynamicFilters = [
  sql`somecol = ${somevalue}`,
  sql`col2 = ${v2}`
];
const dynamicColumns = [sql('somecol'), sql('col2')]
await sql`
  select ${sql.join(dynamicColumns, sql`, `)} from t
  where ${sql.join(dynamicFilters, sql` and `)};
`;

No file or test is named in the issue. Start by tracing how postgres.js handles tagged templates, nested SQL partials, and parameter collection; then define the join behavior from the dynamic columns and filters examples, including delimiters and parameterized parts, and add coverage for those cases.