Support for native AOT & static linking

[andrewmd5]

Gives consumers of wasmtime-dotnet the ability to statically link the native libraries into their executable when publishing with AOT compilation.

I also added all the necessary attributes on the reflection codepaths.

using System;
using System.Diagnostics.CodeAnalysis;
using Wasmtime;

[assembly: UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Wasmtime callback wrappers work correctly with AOT")]
[assembly: UnconditionalSuppressMessage("AOT", "IL3050", Justification = "Wasmtime callback wrappers work correctly with AOT")]

const string wat = """
(module
  ;; Import the hello function from C#
  (import "" "hello" (func $hello))
  ;; Import the add function from C#
  (import "" "add" (func $add (param i32 i32) (result i32)))
  ;; Export a run function that calls hello
  (func (export "run")
    call $hello
  )
  ;; Export a test_math function that uses add and returns a value
  (func (export "test_math") (result i32)
    ;; Call add(10, 32) and return the result (should be 42)
    i32.const 10
    i32.const 32
    call $add
  )
)
""";

Console.WriteLine("Loading WebAssembly module from embedded WAT");
using var engine = new Engine();
using var module = Module.FromText(engine, "hello", wat);
using var linker = new Linker(engine);
using var store = new Store(engine);

linker.Define(
    "",
    "hello",
    Function.FromCallback(store, () => Console.WriteLine("Hello from C#, WebAssembly!"))
);

linker.Define(
    "",
    "add",
    Function.FromCallback(store, (int a, int b) => {
        var sum = a + b;
        Console.WriteLine($"C# add function: {a} + {b} = {sum}");
        return sum;
    })
);

var instance = linker.Instantiate(store, module);
var run = instance.GetAction("run");
if (run is null)
{
    Console.WriteLine("error: run export is missing");
    return;
}
run();

var mathTest = instance.GetFunction<int>("test_math");
if (mathTest is not null)
{
    var result = mathTest();
    Console.WriteLine($"test_math returned: {result}");
}
else
{
    Console.WriteLine("warning: test_math export is missing");
}

Console.WriteLine("All tests completed successfully!");

produces:

➜  wasmtime-dotnet git:(main) /Users/andrew/projects/wasmtime-test/bin/Release/net9.0/osx-arm64/publish/test
Loading WebAssembly module from embedded WAT
Hello from C#, WebAssembly!
C# add function: 10 + 32 = 42
test_math returned: 42
All tests completed successfully!
➜  wasmtime-dotnet git:(main) otool -L /Users/andrew/projects/wasmtime-test/bin/Release/net9.0/osx-arm64/publish/test
/Users/andrew/projects/wasmtime-test/bin/Release/net9.0/osx-arm64/publish/test:
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1356.0.0)
        /usr/lib/libobjc.A.dylib (compatibility version 1.0.0, current version 228.0.0)
        /usr/lib/swift/libswiftCore.dylib (compatibility version 0.0.0, current version 0.0.0)
        /usr/lib/swift/libswiftFoundation.dylib (compatibility version 1.0.0, current version 120.100.0)
        /usr/lib/libicucore.A.dylib (compatibility version 1.0.0, current version 76.1.0)
        /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 4103.0.0)
        /System/Library/Frameworks/CryptoKit.framework/Versions/A/CryptoKit (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (compatibility version 300.0.0, current version 4103.0.0)
        /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 61901.40.47)
        /System/Library/Frameworks/GSS.framework/Versions/A/GSS (compatibility version 1.0.0, current version 1.0.0)
➜  wasmtime-dotnet git:(main)

My recommendation would be to drop support for .NET Standard 2.1 to take advantage of static abstract members in interfaces to avoid using things like Activator.CreateInstance - and introduce a source generator to to remove all dependencies on reflection. But for my use-case this PR is sufficient and unblocks me.

Resolves #293

[andrewmd5]

CC: @peterhuene & @jsturtevant

[martindevans]

My recommendation would be to drop support for .NET Standard 2.1

Personally I would like to keep keep .NET Standard 2.1 support until Unity supports CoreCLR, after that I wouldn't have a usecase for it. Anyone stuck using .NET Framework would probably want it kept beyond that.