VReplication: handle escaped identifiers in vschema when initializing sequence tables

[mattlord]

Description

This work ensures that VReplication — when initializing sequence tables during a traffic switch — handles any escaped identifiers (by unescaping them) that may be in the vschema while continuing to ensure that they are escaped when using them in SQL queries.

This PR also moves more of the VReplication endtoend tests to vtctldclient as we now escape the backing sequence table customer_seq references in the test vschemas and the vtctlclient (wrangler) implementation remains unchanged as it's long deprecated and should be removed entirely in v21 or v22.

I think that this is worth back porting to the latest GA release (v20), for RC2 if we can.

Related Issue(s)

• Fixes: VReplication SwitchTraffic: backticks in sequence tables in vschema cause SwitchTraffic to error out #16160

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

[vitess-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 49.36709% with 40 lines in your changes missing coverage. Please review.

Project coverage is 68.59%. Comparing base (13846e6) to head (990cc6a).
Report is 2 commits behind head on main.

Files	Patch %	Lines
go/vt/vtctl/workflow/traffic_switcher.go	50.00%	39 Missing ⚠️
go/vt/vttablet/tabletserver/schema/engine.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16169      +/-   ##
==========================================
+ Coverage   68.57%   68.59%   +0.01%     
==========================================
  Files        1544     1544              
  Lines      197863   197918      +55     
==========================================
+ Hits       135688   135757      +69     
+ Misses      62175    62161      -14     

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[mattlord]

The timeout was extended for unit tests in https://github.com/vitessio/vitess/pull/15797/files#diff-470746102447655f4af9e1e9c9756444906143d6b70e394d42eff2aa251fa05aR87 but the race one was not (it should have been — I think that change was made in parallel with them getting split).