made CTEs and some columns use alias, eliminate whitespace

[heavycrystal]

This is part of a series of PRs to address the size of our BigQuery merge statements. The maximum supported size for a single BQ query is 1MB and really wide tables with a lot of TOAST columns can cause our merge statement generator to generate queries that BigQuery cannot execute.

For this PR:

1. Remove unnecessary whitespace in merge statements.
2. Change our CTEs to use shorter aliases, _peerdb_deduped -> _d etc.
3. Alias some of our frequently used raw table columns: _peerdb_unchanged_toast_columns -> _ut.