Reasons for carve out:

- It allows us to communicate client stability with semver, instead of all
  clients being contained in a mega v0.Y.Z module.
- It allows us to separate the per-client dependencies.

This CL was created by:

1. Create bigquery/CHANGES.md
2. Create bigquery/go_mod_tidy_hack.go
3. Run:

    cd bigquery
    go mod init cloud.google.com/go/bigquery
    go mod edit -require cloud.google.com/[email protected]
    go mod edit -replace cloud.google.com/[email protected]=../
    go mod tidy
    go mod edit -dropreplace cloud.google.com/[email protected]
    cd ..
    go mod tidy

Also backfills notes to CHANGES.md and backfills datastore/CHANGES.md.

This CL will be tagged v0.44.2 and bigquery/v1.0.0.

Change-Id: I8c976a9f9b5ed1831924b0af5bfb30d5b69e8450
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/43870


Reviewed-by: Tyler Bui-Palsulich <[email protected]>