Topojson regroup several libraries (topojson, topojson-server, topojson-simplify, topojson-client, topojson-specification). The actual typing definition contain them all making it immpossible to use them separately (#24941). This PR extract topojson-client, topojson-simplify and topojson-specification in their own type definition.

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• Test the change in your own code. (Compile and run.)
• Add or edit tests to reflect the change. (Run with npm test.)
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• Avoid common mistakes.
• Run npm run lint package-name (or tsc if no tslint.json is present).

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If adding a new definition:

• The package does not already provide its own types, or cannot have its .d.ts files generated via --declaration
• If this is for an NPM package, match the name. If not, do not conflict with the name of an NPM package.
• Create it with dts-gen --dt, not by basing it on an existing project.
• tslint.json should be present, and tsconfig.json should have noImplicitAny, noImplicitThis, strictNullChecks, and strictFunctionTypes set to true.