Avoid const enum in public API declarations

[ajafff]

const enum in declaration files will cause errors in downstream projects that build with --isolatedModules.

There are two possible solutions:

• forbid export const enum entirely
• modify declaration files before publish / after build (like TypeScript does)
  • needs preserveConstEnums

However this is fixed, it needs to be done in upstream dependencies as well (tsutils).

Related discussion: microsoft/TypeScript#20703

[ajafff]

microsoft/TypeScript#28465 makes it so that there's no error when const enum is merely present in any declaration file. Instead you simply cannot use it.

It still makes sense to avoid const enum in the public API. The inlining of const enum makes it impossible to change its values in a minor or patch release.