c#: Encode version in namespace to support wit versions

[jsturtevant]

Prior to this change the multi-version wit was putting the functions from different versions into the same class which was causing the test to fail as there were multiple implementations of the same function:

C:\Users\jstur\projects\wit-bindgen\target\codegen-tests\guest-csharp-multiversion\foo\Wit.imports.my.dep.AInterop.cs(25,27): error CS0102: The type 'AInterop' already contains a definition for 'XInterop' [C:\Users\jstur\projects\wit-bindgen\target\codegen-tests\guest-csharp-multiversion\foo\TheWorld.csproj]
C:\Users\jstur\projects\wit-bindgen\target\codegen-tests\guest-csharp-multiversion\foo\Wit.imports.my.dep.AInterop.cs(31,33): error CS0111: Type 'AInterop' already defines a member called 'X' with the same parameter types [C:\Users\jstur\projects\wit-bindgen\target\codegen-tests\guest-csharp-multiversion\foo\TheWorld.csproj]
C:\Users\jstur\projects\wit-bindgen\target\codegen-tests\guest-csharp-multiversion\foo\Wit.imports.my.dep.AInterop.cs(28,36): error CS0111: Type 'AInterop.XInterop' already defines a member called 'wasmImportX' with the same parameter types [C:\Users\jstur\projects\wit-bindgen\target\codegen-tests\guest-csharp-multiversion\foo\TheWorld.csproj]

Now the it generates a file for each version (if present) with the functions namespaced by version:

wit_foo.wit.imports.my.dep.v0_1_0.A;

It also creates a file per version:

To note:

• namespaces parts can't start with numbers so put v in front.
• This also lowercases all the names in the namespace, but we had a mixture of upper and lower case so this makes it atleast consistent. Can maybe follow up to make it more csharp like

[jsturtevant]

The refactor here exposed an issue with the way namespaces and files where generating:

Prior to this change (on main) we were getting files like

namespace wit_w.wit.exports.name3Name3Name3;

## file name
Wit.exports.name3Name3Name3.cs

Now we get

namespace wit_w.wit.exports.name3.name3.Name3;

## file name
Wit.exports.name3.name3.Name3.cs

Which is actual what we really want. With #782 and a small tweak to the import Interop class this will pass

[jsturtevant]

has cherry-pick from #782

[silesmo]

Looks good. Thank you!

[yowl]

Thanks!