[Neo Core Style] Rename parameters, update comments, fix code style

[Jim8y]

Description

This pr is mainly intended to rename the index to blockHeight. Reason of making this update is because when we use

    public static Manifest.ContractManifest Manifest { get; } =
        NativeContract.Ledger.GetContractState(ProtocolSettings.Default, uint.MaxValue).Manifest;

the second parameter is confusing, as native contract itself has a field Id, sort of confusing to people who is not familer with neo as core-devs. Well, i am also lost for a while thought shargon was passing the contract id/index in the devpack test engine.

And to avoid this pr be a single line pr, I also fixed some style issues, and a nullable issue here:

.Concat(_eventsDescriptors != null ? _eventsDescriptors.Select(u => u.ActiveIn) : [])

As Concat requires left and right value both be NotNull while _eventsDescriptors is nullable.

Fixes # (issue)

Type of change

• Optimization (the change is only an optimization)
• Style (the change is only a code style for better maintenance or standard purpose)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Existing tests.

Test Configuration:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules