tests: test prewrite and commit out of order before initialized (#1319)

[ti-srebot]

cherry-pick #1319 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In ticdc repo:
git pr https://github.com/pingcap/ticdc/pull/1333

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/ticdc.git pr/1333:release-4.0-30fbd24492d9

---

What problem does this PR solve?

Improve unit test of kv client, part of #1292

What is changed and how it works?

• Test kv client can handle out of order prewrite and commit before initialized properly
• Test txn heartbeat event, which is a prewrite without value
• Test rollback event

Check List

Tests

• Unit test
• Integration test

Release note

• No release note

[ti-srebot]

/run-all-tests

[codecov-io]

Codecov Report

Merging #1333 (6e4b2e4) into release-4.0 (f28608b) will increase coverage by 0.1071%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##           release-4.0      #1333        +/-   ##
===================================================
+ Coverage      46.9692%   47.0763%   +0.1071%     
===================================================
  Files              130        130                
  Lines            13066      13066                
===================================================
+ Hits              6137       6151        +14     
+ Misses            6264       6249        -15     
- Partials           665        666         +1     

[amyangfei]

/merge

[ti-srebot]

/run-all-tests