Split historyEngine.go into small files

[taylanisikdemir]

What changed?
historyEngine.go is a giant file with ~4k lines which makes it hard to maintain/review and add tests for.
Splitting to small files (mostly one file per public method) to make it more testable.

There are 3 separate test suites with some overlap of what they are testing

• engineSuite
• engine2Suite
• engine3Suite

In follow up PRs we are going to add test files for each file and split (get rid of) those suites as well.

Why?
Make it more readable and testable

How did you test it?
unit tests

[codecov]

Codecov Report

Attention: Patch coverage is 40.20530% with 1398 lines in your changes are missing coverage. Please review.

Project coverage is 63.97%. Comparing base (a843a9e) to head (d115906).
Report is 1 commits behind head on master.

❗ Current head d115906 differs from pull request most recent head f57c17b. Consider uploading reports for the commit f57c17b to get more accurate results

Additional details and impacted files

Files	Coverage Δ
.../engine/engineimpl/record_decision_task_started.go	100.00% <100.00%> (ø)
...gine/engineimpl/respond_decision_task_completed.go	100.00% <100.00%> (ø)
...y/engine/engineimpl/remove_signal_mutable_state.go	85.71% <85.71%> (ø)
.../engine/engineimpl/respond_decision_task_failed.go	0.00% <0.00%> (ø)
...tory/engine/engineimpl/cross_cluster_operations.go	0.00% <0.00%> (ø)
service/history/engine/engineimpl/reset_queues.go	0.00% <0.00%> (ø)
...history/engine/engineimpl/reset_sticky_tasklist.go	0.00% <0.00%> (ø)
...ine/engineimpl/record_child_execution_completed.go	77.41% <77.41%> (ø)
...gine/engineimpl/respond_activity_task_completed.go	74.19% <74.19%> (ø)
...rvice/history/engine/engineimpl/describe_queues.go	0.00% <0.00%> (ø)
... and 20 more

... and 6 files with indirect coverage changes

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