Typescript export default erased in presence of namespace

[Wolvereness]

Bug Report

Current Behavior

The presence of a declare namespace where the name is shared erases the export default.

export class N {
  f1(value) {
    value.f2();
  }

}

Input Code

export class N {
    f1(value: N.I) {
        value.f2();
    }
}
export declare namespace N {
    export interface I {
        f2();
    }
}
export default N;

Expected behavior/code

export class N {
  f1(value) {
    value.f2();
  }

}

export default N;

Babel Configuration (.babelrc, package.json, cli command)

{
  "your": { "config": "here" }
}

Environment

• Babel version(s): a596da2
• Node/npm version: v8.12.0
• OS: Windows 10
• Monorepo: ?
• How you are using Babel: cli fixtures

Possible Solution

Same solution.

Independently: #10034

Required for: #9785

Additional context/Screenshots

Introduced in #10019

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