Add linked editing support

[tsmaeder]

Feature Description:

Add support for linked editing. Linked editing is supported in the version of monaco we use: https://github.com/theia-ide/vscode/blob/standalone/0.23.x/src/vs/editor/standalone/browser/standaloneLanguages.ts#L427

The tasks would be:

1. Add the types and functions from the above reference to packages\monaco\src\typings\monaco\index.d.ts
2. Add Types LinkedEditingRanges and LinkeEditingRageProvider to theia.d.ts
3. Add registerLinkedEditingRangeProvider to the languages API namespace and implement registration analog to other editor features.