Only default to csv or multi if the type was array (#4118)

Some emitters are doing some bad things and not respecting the real
meaning of format. To try to reduce breaking change we will only set the
format if the type was an array which is when you needed to use it
before

.chronus/changes/fix-tsp-default-csv1-2024-7-7-14-31-14.md

@@ -0,0 +1,6 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/http"
+---
+

packages/http/src/decorators.ts

@@ -144,9 +144,19 @@ export const $query: QueryDecorator = (
     type: "query",
     explode:
       userOptions.explode ?? (userOptions.format === "multi" || userOptions.format === "form"),
-    format: userOptions.format ?? (userOptions.explode ? "multi" : "csv"),
+    format: userOptions.format,
     name: paramName,
   };
+
+  if (
+    entity.type.kind === "Model" &&
+    isArrayModelType(context.program, entity.type) &&
+    // eslint-disable-next-line deprecation/deprecation
+    options.format === undefined
+  ) {
+    // eslint-disable-next-line deprecation/deprecation
+    options.format = userOptions.explode ? "multi" : "csv";
+  }
   context.program.stateMap(HttpStateKeys.query).set(entity, options);
 };