Add swift-format lint issues in the problems view

[adam-fowler]

Is your feature request related to a problem? Please describe.
As more projects move to using swift-format they will also be using swift-format lint. Currently there is no way to view swift-format lint issues in VSCode. Quite a number of the Apple open source projects eg swift-nio use swift-format lint already.

Describe the solution you'd like
On saving a file run swift-format lint and any issues found should be added to the problems view.

There might be issues if the user has swift-format formatting on file save enabled. You'd want to be sure you are reading the version of the file after the format has been run.

[award999]

Raised issue for what we need from the LSP swiftlang/sourcekit-lsp#2166