Support WASI snapshot0 in the C API.

This commit adds support for snapshot0 in the WASI C API.

A name parameter was added to `wasi_instance_new` to accept which WASI module
is being instantiated.

Additionally, the C# API now supports constructing a WASI instance based on the
WASI module name.

Fixes #1221.

crates/misc/dotnet/src/Interop.cs

@@ -936,6 +936,7 @@ namespace Wasmtime
         [DllImport(LibraryName)]
         public static extern WasiInstanceHandle wasi_instance_new(
             StoreHandle store,
+            [MarshalAs(UnmanagedType.LPUTF8Str)] string name,
             WasiConfigHandle config,
             out IntPtr trap
         );

crates/misc/dotnet/src/Wasi.cs

@@ -9,18 +9,26 @@ namespace Wasmtime
         /// <summary>
         /// Creates a default <see cref="Wasi"/> instance.
         /// </summary>
-        public Wasi(Store store) :
+        /// <param name="store">The store to use for the new WASI instance.</param>
+        /// <param name="name">The name of the WASI module to create.</param>
+        public Wasi(Store store, string name) :
             this(
                 (store ?? throw new ArgumentNullException(nameof(store))).Handle,
-                Interop.wasi_config_new()
+                Interop.wasi_config_new(),
+                name
             )
         {
         }
 
-        internal Wasi(Interop.StoreHandle store, Interop.WasiConfigHandle config)
+        internal Wasi(Interop.StoreHandle store, Interop.WasiConfigHandle config, string name)
         {
+            if (string.IsNullOrEmpty(name))
+            {
+                throw new ArgumentException("Name cannot be null or empty.", nameof(name));
+            }
+
             IntPtr trap;
-            Handle = Interop.wasi_instance_new(store, config, out trap);
+            Handle = Interop.wasi_instance_new(store, name, config, out trap);
             config.SetHandleAsInvalid();
 
             if (trap != IntPtr.Zero)

crates/misc/dotnet/src/WasiBuilder.cs

@@ -12,10 +12,22 @@ namespace Wasmtime
         /// <summary>
         /// Constructs a new <see cref="WasiBuilder" />.
         /// </summary>
-        public WasiBuilder()
+        public WasiBuilder(string name)
         {
+            if (string.IsNullOrEmpty(name))
+            {
+                throw new ArgumentException("Name cannot be null or empty.", nameof(name));
+            }
+
+            Name = name;
         }
 
+        /// <summary>
+        /// Gets the name of the WASI module being built.
+        /// </summary>
+        /// <value>The name of the WASI module.</value>
+        public string Name { get; private set; }
+
         /// <summary>
         /// Adds a command line argument to the builder.
         /// </summary>
@@ -271,7 +283,7 @@ namespace Wasmtime
             SetStandardError(config);
             SetPreopenDirectories(config);
             
-            return new Wasi(store.Handle, config);
+            return new Wasi(store.Handle, config, Name);
         }
 
         private unsafe void SetConfigArgs(Interop.WasiConfigHandle config)