Stop the F# wrapper hardcoding its documentation path

[Rafael-SOWNet]

dotnet build -c release — lowercase — cannot build AngouriMath.FSharp from a clean checkout on
Linux or macOS:

FSC : error FS0193: Could not find a part of the path
'.../Sources/Wrappers/AngouriMath.FSharp/bin/Release/netstandard2.0/AngouriMath.FSharp.XML'

Cause

The fsproj set the documentation path literally:

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
  <DocumentationFile>bin\Release\netstandard2.0\AngouriMath.FSharp.XML</DocumentationFile>
</PropertyGroup>

MSBuild compares strings in a Condition case-insensitively, so with -c release the condition
matches and DocumentationFile points at bin/Release/…. But $(OutputPath) is built from the
configuration as spelled, so the directory that actually gets created is bin/release/. On a
case-sensitive filesystem those are two different paths, the second does not exist, and the F#
compiler cannot create the file in it.

Fix

<GenerateDocumentationFile>true</GenerateDocumentationFile>, which puts the XML beside the
assembly whichever way the configuration is spelled and needs no path. AngouriMath.Terminal.Lib
already does exactly this, so it is the in-repo precedent rather than a new idea. The main library
was never affected — it uses bin/$(Configuration)/$(TargetFramework)/…, which follows the spelling.
AngouriMath.FSharp was the only project with a literal.

Verified from a clean bin and obj, both spellings

dotnet test -c release	130 passed, 0 failed — this is the command that used to fail
dotnet build -c Release	succeeds, and still produces AngouriMath.FSharp.xml and AngouriMath.FSharp.2.0.0.nupkg

So packaging is unchanged; the only difference is that the file is now .xml rather than .XML,
which is what every other project here already emits.

Why nobody hit it

-c Release works, and -c release also works once a capitalised build has created the
directory. It fails only on a clean checkout that has never been built with the capitalised
spelling — which is what CI would do if it ever used the lowercase form, and what I did while
measuring #888. It cost a measurement I had to redo: the first run reported the F# suite as having
been exercised when the build had in fact failed, which is the trap in
dotnet test reusing whatever assembly is already there.