chore(lint): add no-const-enum rule

[cartant]

Description:

This PR enables the no-const-enum rule that's in tslint-etc.

ATM, tslint-etc is used in the dtslint tests to catch malformed type expectations. This PR bumps the tslint-etc version and enables the above-mentioned rule in the project's tslint.json file.

The reason const enums cannot be used is outlined in #4556. Basically, using a const enum prohibits isolated module transpilation, as it's necessary to refer to another file to determine the literal that should replace a reference to a const enum member. That means that versions of RxJS that export const enums cannot be used with create-react-app-generated projects or any other projects that build using isolated modules.

As configured, the rule forbids all use of const enums. The rule does have an allowLocal option, but I don't see the use of local (i.e. within a single module) const enums to be a likely use case.

The main reason for adding the rule is to prevent the sort of breaking change that happened in 6.4.0 from happening again. In #4556, I mentioned that I tried to include a test that compiled the project using isolated modules, but was unable to do so (the reason is given in the linked PR).

The linting in this PR will fail until #4556 is merged.

Related issue (if exists): #4556

[coveralls]

Pull Request Test Coverage Report for Build 8298

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 10 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.2%) to 96.677%

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Files with Coverage Reduction	New Missed Lines	%
src/internal/operators/partition.ts	1	75.0%
src/internal/operators/repeatWhen.ts	1	95.71%
src/internal/OuterSubscriber.ts	1	50.0%
src/internal/observable/fromObservable.ts	3	0.0%
src/internal/operators/onErrorResumeNext.ts	4	81.82%

Totals
Change from base Build 8294:	-0.2%
Covered Lines:	5208
Relevant Lines:	5387

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💛 - Coveralls

[cartant]

Aarrgghh! I rebased and force pushed the branch that I had on this notebook and managed to wipe my commits, as this notebook must have had a branch with no work in it. Or something. Will have to fix this later, when I get home. Hopefully, the work will be on my other notebook.