Update FSharp.Compiler.Service to version 34.0.1

[baronfel]

This brings along some perf improvements, as well as a slew of syntax features and preview features that have been merged in the last few months.

I added support for the LangVersion option to the MirrorSharpFsharpOptions as well, which enables people to use any of the features gated by specific language version/preview support: feature list

[baronfel]

I'm not sure how support for LangVersion would flow through sharplab specifically, though.

Another thing I noticed: it looks like in sharplab the F# support is using .Net Framework instead of .Net Core assemblies? If that's right I can help fix that.

[ashmind]

Thanks! Looks good -- I'll take a look soon.
I just caused some conflicts by updating master, but I should be able to resolve them.

For SharpLab:

1. LangVersion is normally set to the current maximum value -- I can set that to 9999
2. SharpLab has both .NET Core and .NET Framework sites depending on what you select in dropdown -- each one should use corresponding platform for F#?

[baronfel]

LangVersion should probably just be 'preview' for us, then. This includes all present and future language enhancements. Re: .Net Core/.Net Framework: there's a --targetprofile command line setting that should vary based on that choice. It should be --targetprofile:netcore for .net core, and --targetprofile:mscorlib for .net framework. I'll get the correct value and update here.

[ashmind]

Thanks -- do you want to include --targetprofile in this PR? If so I'll not merge until that's added.

[baronfel]

I went ahead and added it.

The valid values are (taken from the F# compiler codebase):

// Indicates we assume "mscorlib.dll", i.e .NET Framework, Mono and Profile 47
| "mscorlib" -> PrimaryAssembly.Mscorlib
// Indicates we assume "System.Runtime.dll", i.e .NET Standard 1.x, .NET Core App 1.x and above, and Profile 7/78/259
| "netcore"  -> PrimaryAssembly.System_Runtime
// Indicates we assume "netstandard.dll", i.e .NET Standard 2.0 and above
| "netstandard"  -> PrimaryAssembly.NetStandard

but all code in the compiler uses one of "mscorlib" or "netcore", so for SharpLab that seems a reasonable path to follow.

[ashmind]

I wonder if we want to provide string constants for those, but anyways can always add later.

[joelpryde]

Is there any way to set the TargetProfile for normal CSharp compilation? I can't seem to find that option.