Support for type definition

it's like go to definition but for goes to type definition.
https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_typeDefinition


https://user-images.githubusercontent.com/13261088/120936913-c8b2b280-c71f-11eb-936f-f278f00c800f.mp4



This is an example from vim with ocaml.