Fix error when exporting const enums (#33060)

[EvanCahill]

Const enums should be allowed to be exported using an export declaration. The fix is to remove an incorrect check that restricts exporting const enums in export declarations to work only when --preserveConstEnums is true.

Fixes #33060

[weswigham]

Actually, you do need preserveConstEnums on. If you don't, the enum declaration will be erased, but the export declaration will still emit something along the lines of

exports.MyConstEnum = MyConstEnum;

which is going to throw at runtime, as MyConstEnum won't exist. (?)

[EvanCahill]

I don't see that as the behavior currently. It is correctly eliding the const enum export.

[weswigham]

Oh, hum. I guess if we're already eliding the export then it's not so bad.

[EvanCahill]

I'm happy to add another test case to explicitly test that const enums are not emitted on re-export without preserveConstEnums.

Also I'd really love this to go into 3.7 if everything looks good since this behavior is a regression from 3.5.

[weswigham]

A new test'd be great, yeah.

[EvanCahill]

Done.

[weswigham]

cc @RyanCavanaugh do we wanna do anything with this for 3.7?

[DanielRosenwasser]

@typescript-bot cherry-pick this to release-3.7 and LKG

[typescript-bot]

Heya @DanielRosenwasser, I couldn't find the branch 'release-3.7' on Microsoft/TypeScript. You may need to make it and try again.

[DanielRosenwasser]

Ugh, come on, ignore the backticks you jerk robot.

@typescript-bot cherry-pick this to release-3.7 and LKG

[typescript-bot]

Hey @DanielRosenwasser, I've opened #34811 for you.