[api-extractor-model] Remove "const" keyword before enum to use with typescript isolatedModules

[samisayegh]

Summary

When a typescript project is using isolatedModules, referencing exported const enums is not allowed.

Details

Setting isolatedModules to true is recommended for projects transpiled with babel or esbuild. Unlike tsc, these tools evaluate files independently. Setting the isolatedModules flag e.g. forces developers to indicate whether they are exporting a type or value, since transpilers evaluating modules independently cannot infer this information.

However, the flag also alerts when a const enum is used. It seems that tsc evaluates const enums across modules and inlines the constants at compile. No enum object is created, which is problematic of independent transpilation.

I found this article helpful for understanding the effect of specifying const.

By removing the const keyword, the enums can safely be used in projects using isolatedModules. This change is similar to this recent PR.

How it was tested

I used npm link and no longer saw the error. Note also that I did not face the error with the ReleaseTag enum which is not using const.

[ghost]

All CLA requirements met.

[samisayegh]

When running rush change on the forked repo, I see the following error:

Not sure what to do hmm

Edit: I ran the command in the original repo and copied the generated dir into the forked repo.