Client side gutter icons

[keyboardDrummer]

Changes

• Compute gutter icons on the client and configure the server so it no longer sends gutter icons to the client.

Here's an example. Left shows client side computed icons, and right shows server side computed icons (using latest nightly):

Client computed	Server computed

Left seems more correct, since right indicates errors on line 18 and 20 event though verification found no errors there. Also, left finds proven assertion on line 33 that right does not find.

Testing

• Manual testing looked good, although I'm sure there are small differences. @MikaelMayer could you also manually test this PR ?
• Added unit tests for the method computeNewGutterIcons, to check that given the particular symbolStatus, diagnostics and documentSymbol information, the right gutter icons are computed.
• Did not add an integration test that runs an actual language server and checks that the icons per line evolve according to expectations. Such a test would be difficult to make stable because it depends on having a running language server.

[MikaelMayer]

I just tried this PR with the latest Dafny master. I typed:

method Test() {

}

and got the following result

Reloading VSCode on that same file displays nothing in gutter icons.
Even writing "assert true;" inside did not change anything.

The language server was started with these options.

Language server: {"command":"...\\AppData\\Local\\Temp\\vscode-dafny-dlls-W1YBH8\\Dafny.exe","args":["server","--verify-on:Change","--verification-time-limit:30","--cache-verification=0","--cores:4","--notify-ghostness:true","--notify-line-verification-status:false"]}
Dafny is ready

[MikaelMayer]

Also, what about backward compatibility? We can assume users will always use the most up to date version of VSCode, but not that they will use the most up to date version of Dafny for quite a long time (I've seen migrations lasting 1 year!)
What earliest version of Dafny is your change supporting?

[keyboardDrummer]

I'm in a branch that includes my unmerged PRs to Dafny server. Will let you know when those are merged.

Given the code you showed, when opening the file I get:

When pressing verification it turns into:

---

Different contents:

With manual verification, on opening file:

After clicking verify:

or with an extra newline: