JSON Language Server doesn't declare formatting capabilities as result of initialize

[mickaelistria]

Using VSCode 1.33, I'm trying to use the included JSON Language Server in another client supporting LSP (Eclipse Wild Web Developer if you're curious). It provides a lot of value already.
However, formatting is not declared as a capability, although the LS manages to format correctly. The reason is that, as we can see in https://github.com/Microsoft/vscode/tree/master/extensions/json-language-features/server/README.md, formatting seems only enabled through dynamicRegistration. This doesn't seem necessary and declaring capability statically would be much simpler.

[aeschli]

I added a new initialization option to the server:

• provideFormatter: boolean | undefined. If defined, the value defines whether the server provides the documentRangeFormattingProvider capability on initialization. If undefined, the setting json.format.enable is used to determine whether formatting is provided. The formatter will then be registered through dynamic registration. If the client does not support dynamic registration, no formatter will be available.