Track and join pending database transaction when using transactWithRetry

[isoos]

Note: typed_sql (or specifically the postgresql driver) doesn't support re-entrant calling of db.transact(). With this change we don't force-start a new transaction, just use the outer one (same logic as with joining the outermost retry block).

[jonasfj]

Note: typed_sql (or specifically the postgresql driver) doesn't support re-entrant calling of db.transact(). With this change we don't force-start a new transaction, just use the outer one (same logic as with joining the outermost retry block).

I think it's only concurrent nested subtransactions that disallowed.

[jonasfj]

See also google/dart-neats#372

That said, one can argue that we probably don't need nested transactions, and instead just want single transactions.

Where in our code is this even relevant?

[isoos]

Note: this may not be needed after all. Though, we could use this to detect re-entrant transaction calls, which we probably don't want, and maybe block them?