Incorporate last round of Spec team discussion

Expand the full form to include `Params` as an intermediate term in the
signature, so that other things can slot in as peers to it in the
future if or when that makes sense, and so that it makes sense what
exactly is being named as a `Positional` field there.

text/0748-glimmer-component-signature.md

@@ -113,7 +113,9 @@ Two points to notice about the signature:
 // arguments, and could be reused for helpers, modifiers, etc.
 interface InvokableSignature {
   Args?: {
-    Named?: Record<string, unknown>;
+    Named?: {
+      [argName: string]: unknown;
+    };
     Positional?: unknown[];
   };
 }
@@ -123,14 +125,18 @@ interface InvokableComponentSignature extends InvokableSignature {
   Element?: Element | null;
   Blocks?: {
     [blockName: string]: {
-      Positional?: unknown[];
+      Params?: {
+        Positional?: unknown[];
+      };
     }
   }
 }
 
 interface InvokableGlimmerComponentSignature extends InvokableComponentSignature {
   Args?: {
-    Named?: Record<string, unknown>;
+    Named?: {
+      [argName: string]: unknown;
+    };
     // empty tuple here means it does not allow *any* positional params
     Positional?: [];
   }
@@ -150,8 +156,8 @@ interface GlimmerComponentSignature {
     [argName: string]: unknown;
   };
   Blocks?: {
-    [blockName: string]: unknown[]
-  }
+    [blockName: string]: unknown[];
+  };
   Element?: Element | null;
 }
 ```