Revert "Revert "Parse v2 record. (#35408)" (#35469)"

[changliiu]

No implementation change.

Only changes:

1. remove pined proto version
2. update the ChangeStreamrecordMapper comments.

Reverts #35469
#35480 should solve the dependency issue in the original reverted PR #35408

[github-actions]

Assigning reviewers:

R: @ahmedabu98 for label java.
R: @nielm for label spanner.

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