support propertyOrder for completions

Is your enhancement related to a problem? Please describe.

JSONSchema supports propertyOrder, which acts as an aid for UIs to perform completions in the order as was intended by the developer. This is incredibly useful for users as it makes creating a YAML from scratch "look" more understandable.

Describe the solution you would like

yamlcompletions that follow the propertyOrder directive in JSON schema

Describe alternatives you have considered

Patch proposed

Additional context

The following would provide this functionality:

diff --git a/src/languageservice/jsonSchema.ts b/src/languageservice/jsonSchema.ts
index e8b6f90..1688a0b 100644
--- a/src/languageservice/jsonSchema.ts
+++ b/src/languageservice/jsonSchema.ts
@@ -19,6 +19,7 @@ export interface JSONSchema {
   definitions?: { [name: string]: JSONSchema };
   description?: string;
   properties?: JSONSchemaMap;
+  propertyOrder?: string[];
   patternProperties?: JSONSchemaMap;
   additionalProperties?: boolean | JSONSchemaRef;
   minProperties?: number;
diff --git a/src/languageservice/services/yamlCompletion.ts b/src/languageservice/services/yamlCompletion.ts
index 701c79f..c216f88 100644
--- a/src/languageservice/services/yamlCompletion.ts
+++ b/src/languageservice/services/yamlCompletion.ts
@@ -298,7 +298,6 @@ export class YamlCompletion {
             }
           }
         }
-
         this.addPropertyCompletions(schema, currentDoc, node, '', collector, textBuffer, overwriteRange);
 
         if (!schema && currentWord.length > 0 && document.getText().charAt(offset - currentWord.length - 1) !== '"') {
@@ -655,7 +654,8 @@ export class YamlCompletion {
       return { insertText, insertIndex };
     }
 
-    Object.keys(schema.properties).forEach((key: string) => {
+    const iterator = schema.propertyOrder !== undefined ? schema.propertyOrder : Object.keys(schema.properties);
+    iterator.forEach((key: string) => {
       const propertySchema = schema.properties[key] as JSONSchema;
       let type = Array.isArray(propertySchema.type) ? propertySchema.type[0] : propertySchema.type;
       if (!type) {

Start in src/languageservice/jsonSchema.ts to inspect the JSONSchema definition, then follow addPropertyCompletions in src/languageservice/services/yamlCompletion.ts. Confirm that YAML completions use propertyOrder when provided and retain the existing property ordering behavior otherwise.