VReplication/OnlineDDL: reordering enum values

[shlomi-noach]

Description

Fixes #15349

This PR builds a test case where an enum's values are reordered, from ('red', 'green', 'blue') to ('blue', 'green', 'red'), and observes how vreplication (in this case via OnlineDDL) handles it.

The behavior before this PR (see test output) is that vcopier will copy enum values by text, and vplayer by ordinal value.

As of this PR, and solved specifically for Online DDL (the problem is irrelevant for other vreplication workflows), vplayer applies enum column changes by writing the logical (string representation, e.g. 'blue') of the column.

The change is actually quite small. A prior work on converting enums to textual columns has already laid the necessary foundation: making vplayer aware of the enum's schema. This is already supported by setting vreplication's Filter.Rule.ConvertEnumToText map. Previously, we only populated it, as mentioned, when converting enum to text. The only change needed in this PR was to populate it also when an enum remains an enum. Whether the enum's schema is change or not, this ensures applying binlog events from the original table to the target table by enum textual value.

Backport

As this is a corruption bugfix, I believe this should be backported to all supported versions.

Related Issue(s)

• OnlineDDL/VReplication: inconsistency between vcopier & vplayer when copying shuffled enum values #15349
• Feature Request: schemadiff strategy for enum/set value ordinal change #15105
• schemadiff: EnumReorderStrategy, checking if enum or set values change ordinal #15106

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 65.42%. Comparing base (d8f771c) to head (4fd765e).

Files	Patch %	Lines
go/vt/vttablet/onlineddl/vrepl.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15103      +/-   ##
==========================================
+ Coverage   65.39%   65.42%   +0.02%     
==========================================
  Files        1561     1561              
  Lines      193524   193526       +2     
==========================================
+ Hits       126563   126609      +46     
+ Misses      66961    66917      -44     

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[shlomi-noach]

Here is the expected test failure: https://github.com/vitessio/vitess/actions/runs/7736886979/job/21094946752?pr=15103

[shlomi-noach]

This added test is mostly irrelevant to the changes in this PR, but while writing the PR I noticed how this was missing.

[shlomi-noach]

Subsequently to the main change in this PR, it's now fine to reorder enum values, and the default schemadiff hints enum-reordering strategy is now EnumReorderStrategyAllow

[dbussink]

Ah, great that tracking the schema is already solved. That makes this much easier!

[shlomi-noach]

I believe we should backport this to all supported versions, as this is a bugfix in OnlineDDL/VReplication.