Add Map / indexed object support for TypeScript parser

[christophpurrer]

Summary: Changelog: [General][Fixed] [react-native-codegen] react-native-codegen : Add Map / indexed object support for TypeScript parser

In flow we can expose Maps via the following syntax in TM specs

+getMap: (arg: {[key: string]: ?number}) => {[key: string]: ?number};

In TypeScript writing the same spec:

readonly getMap: (arg: { [key: string]: number | null; }) => { [key: string]: number | null; };

leads to an exception the TypeScript code-gen parser

    at react-native-github/packages/react-native-codegen/src/parsers/typescript/modules/index.js:309:23```

This change fixes the TypeScript parser

Reviewed By: cipolleschi

Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was exported from Phabricator. Differential Revision: D40753368

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This pull request was successfully merged by Christoph Purrer in 87c356d56c73c3289da3d5911288909720b11994.

^{When will my fix make it into a release? | Upcoming Releases}