Refactor ID Serial 2: change all IDs to CamelCase

[guoyuhong]

What do these changes do?

Related issue number

Linter

• I've run scripts/format.sh to lint the changes in this PR.

[guoyuhong]

There is modin test fail, because the modin has used ray.ObjectID. Modin is another repo, what is the step to fix that?

[AmplabJenkins]

Test FAILed.
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Test FAILed.

[AmplabJenkins]

Test FAILed.
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Test FAILed.

[robertnishihara]

Thanks @guoyuhong, do you prefer ObjectId because it is more consistent with the camelcase that we use in other places (e.g., Gcs)? ObjectID looks better to me since ID is typically capitalized (since it is an acronym).

Regarding the Modin issue, one option would be to comment out that test until it's changed in Modin and then update the version of Modin after that.

[guoyuhong]

I prefer ObjectId a bit, because current Java lint tool require Java code to use ObjectId. That is to say, Java has different Id name than C++ and python.

[raulchen]

Just quickly googled "camel case abbreviations". It seems that different languages and guides have different rules.
I don't have preference. But I think at least we should rename the class methods in id types to use camel case, e.g., UniqueID.FromRandom().

[guoyuhong]

@raulchen OK, that will be done.

[guoyuhong]

Close this PR and move the function CamelCase PR to #4896 .