ApiDocs: more tolerant cross-references

[dsyme]

Cross references are painful in F# tooling until the F# compiler and editor tooling has proper support for resolving non-explicit specifications

Some examples of things we could support in FSharp.Formatting tooling even before the F# compiler emits the right XML.

Types without namespaces:

 <see cref="TestClass"/> --> <see cref="T:TestNamespace.TestClass"/> 

Constructors:

 <see cref="TestClass(int)"/> -->  <see cref="M:TestNamespace.TestClass.#ctor(System.Int32)"/>

Methods without namespace or type name:

 <see cref="GetZero"/> --> <see cref="M:TestNamespace.TestClass.GetZero"/>

Generic methods without namespace, type name or signature:

<see cref="GetGenericValue"/> --> <see cref="M:TestNamespace.TestClass.GetGenericValue``1(``0)"/>

Generic types

 <see cref="GenericClass{T}"/>  -->  <see cref="T:TestNamespace.GenericClass`1"/>