[api-extractor] Roll up of default export is not valid TypeScript

[yacinehmito]

Minimal example

Use the following snippet as entry file.

// index.ts
const example = 'foo'

export default example

This outputs:

// index.d.ts
export declare const default = "foo";

There, the TypeScript compiler errors with "Variable declaration expected" because the variable has the name default. To solve the issue the file must be manually edited as to match the following:

declare const example = "foo";

export default example;

[octogonz]

Thanks for creating a PR!