wasm-compose: implement a new CompositionGraph API. (#807)

This commit implements a new `CompositionGraph` API that allows for building a
composition with more flexibility than what the `ComponentComposer` API
supports.

The `CompositionGraph` is geared towards live-editing of a composition graph.

This commit also reimplements `ComponentComposer` using the composition graph.

The previous instance graph and the encoding implementation for it have been
removed.

crates/wasm-compose/CONFIG.md

@@ -72,7 +72,7 @@ An instantiation has the following fields:
   arguments; argument names match the names of the imports of the dependency being
   instantiated.
 
-Note that the instantiation name `$component` is special and signifies how the input
+Note that the instantiation name `$input` is special and signifies how the input
 component is to be instantiated.
 
 ### Instantiation arguments
@@ -97,7 +97,7 @@ A slightly complex example of configuring instantiations:
 
 ```yaml
 instantiations:
-  $component:
+  $input:
     arguments:
       a: b
   b:
@@ -109,7 +109,7 @@ instantiations:
     dependency: f
 ```
 
-In the above example, the `$component` instantiation (i.e. the root instantiation) has explicitly
+In the above example, the `$input` instantiation (i.e. the root instantiation) has explicitly
 specified that the argument named `a` is to be provided instance `b`.
 
 It also defines an instantiation named `b` which is to be passed an instance export named `e`

crates/wasm-compose/Cargo.toml

@@ -21,6 +21,7 @@ petgraph = "0.6.2"
 log = { workspace = true }
 serde_yaml = "0.8.26"
 clap = { workspace = true, optional = true }
+smallvec = "1.10.0"
 
 [features]
 default = []

crates/wasm-compose/example/server/config.yml

@@ -2,6 +2,6 @@ search-paths:
   - ../service/target/wasm32-unknown-unknown/release
 
 instantiations:
-  $component:
+  $input:
     arguments:
       backend: svc