Update addError to give precedence to newly added schemas

HttpApiSchema.UnionUnify creates a union whose members are listed in the
order of `[...firstArgUnionMembers, ...secondArgUnionMembers]`. When
encoding a union, Schema will try each member in the order that they
appear.

So the `addError` method on each of the HttpApi* classes, by passing the
user-provided schema as a second argument, causes older schemas that
encompass newer schemas to take precedence over the newer ones.

By flipping the argument order, users are now able to use `addError`
with a schema that (partly) encompasses an older one, to override the
encoding behaviour of value conforming to that schema.

Author: Avaq

packages/platform/src/HttpApi.ts

@@ -184,10 +184,10 @@ const Proto = {
       identifier: this.identifier,
       groups: this.groups,
       errorSchema: HttpApiSchema.UnionUnify(
-        this.errorSchema,
         annotations?.status
           ? schema.annotations(HttpApiSchema.annotations({ status: annotations.status }))
-          : schema
+          : schema,
+        this.errorSchema
       ),
       annotations: this.annotations,
       middlewares: this.middlewares

packages/platform/src/HttpApiEndpoint.ts

@@ -771,8 +771,8 @@ const Proto = {
     return makeProto({
       ...this,
       errorSchema: HttpApiSchema.UnionUnify(
+        annotations?.status ? schema.annotations(HttpApiSchema.annotations({ status: annotations.status })) : schema,
         this.errorSchema,
-        annotations?.status ? schema.annotations(HttpApiSchema.annotations({ status: annotations.status })) : schema
       )
     })
   },

packages/platform/src/HttpApiGroup.ts

@@ -307,8 +307,8 @@ const Proto = {
       topLevel: this.topLevel,
       endpoints: this.endpoints,
       errorSchema: HttpApiSchema.UnionUnify(
+        annotations?.status ? schema.annotations(HttpApiSchema.annotations({ status: annotations.status })) : schema,
         this.errorSchema,
-        annotations?.status ? schema.annotations(HttpApiSchema.annotations({ status: annotations.status })) : schema
       ),
       annotations: this.annotations,
       middlewares: this.middlewares