Introduce configuration for "Go to Symbol in Workspace"

[dmgonch]

Allow configuring number of chars user must to type in for "Go to Symbol in Workspace" command to return any results (default is 0 to preserve existing behavior). The reasoning here is that when lots of projects are loaded by OmniSharp it makes little sense to return all symbols discovered. This change should largely address these issues as well: #1243, dotnet/vscode-csharp#1808.
Additionally allow configuring max number of items returned by "Go to Symbol in Workspace" command. Similarly to the above in a big repo returning pages and pages of items in most cases will be wasteful. But default is 0 which is indicates no limit to preserve existing behavior.

[dmgonch]

The related commit on vscode side: dotnet/vscode-csharp#2487

[rchande]

Thanks for the contribution! Some thoughts...

[rchande]

Because we're changing the behavior of the FindSymbols endpoint, I think we do need to version it.

[filipw]

@rchande @akshita31 I somehow missed this PR before.. what is the reason for MinFilterLength to be introduced on a request? If that comes from the request, then the sender of the request should already know better whether a given value should result in request being sent or not.

this specific check doesn't make much sense, we are validating sender's input, based on sender's condition.. https://github.com/OmniSharp/omnisharp-roslyn/pull/1284/files#diff-030b76f11f6d3bc42e70a3cde2a74be9R24

I think the min length should be implemented on the client side in the VS Code extension, and here we could at best have a global setting that would come from omnisharp.json not from the request

[akshita31]

@filipw Agreed. Apologies that this got missed out somehow.

[dmgonch]

@filipw Thanks for the feedback!
@akshita31 I will look into making the change unless this is something you are planning to work on right away.

[filipw]

I already sent a PR here dotnet/vscode-csharp#2625