Simplify history builder

[vytautas-karpavicius]

What changed?
Simplify history builder by:

• Removing redundant new<...> helper functions. Construct event directly in the Add<...> functions.
• Initialize all event attributes using struct initialization syntax instead of setting them one by one.
• Removed unused methods

Why?
Less code to maintain and easier to read.

How did you test it?
Purely refactoring. Existing tests.

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 0180e038-1825-4400-983e-db88437cb661

• 375 of 419 (89.5%) changed or added relevant lines in 1 file are covered.
• 18 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.009%) to 56.858%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
service/history/execution/history_builder.go	375	419	89.5%

Files with Coverage Reduction	New Missed Lines	%
common/task/weightedRoundRobinTaskScheduler.go	1	88.6%
common/task/fifoTaskScheduler.go	4	83.51%
service/history/task/fetcher.go	4	86.15%
common/persistence/nosql/nosqlExecutionStore.go	9	60.03%

Totals
Change from base Build 0180dd57-a86d-49ac-b027-7918f6353dfa:	0.009%
Covered Lines:	83766
Relevant Lines:	147324

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💛 - Coveralls

[mkolodezny]

assuming you checked for "no usages found" of the removed API's