Finalize folding providers #47808
Description
- finish vscode.proposed.d.ts folding provider API and make it public
- uncomment monaco API
- comment on [folding] language-aware folding #3422
- polish LSP proposed API (https://www.npmjs.com/package/vscode-languageserver-protocol-foldingprovider)
- move json folding impl to vscode-json-languageservice
- move html folding impl to vscode-json-languageservice