feat: Make the Filter type more specific. (#915) Thanks to @ylixir

Now the type more accurately represents which Filter objects are valid.
This will provide better code completion, documentation and allow the
typechecker to better help in writing more robust new code and in more
easily refactoring existing code.

Author: ylixir

packages/cubejs-client-core/index.d.ts

@@ -563,12 +563,35 @@ declare module '@cubejs-client/core' {
     annotation(): QueryAnnotations;
   }
 
-  export type Filter = {
+  export type Filter = BinaryFilter | UnaryFilter;
+  type BinaryFilter = {
     dimension?: string;
     member?: string;
-    operator: string;
-    values?: string[];
+    operator: BinaryOperator;
+    values: string[];
   };
+  type UnaryFilter = {
+    dimension?: string;
+    member?: string;
+    operator: UnaryOperator;
+    values?: never;
+  };
+  type UnaryOperator = 'set' | 'notSet';
+  type BinaryOperator =
+    | 'equals'
+    | 'notEquals'
+    | 'contains'
+    | 'notContains'
+    | 'gt'
+    | 'gte'
+    | 'lt'
+    | 'lte'
+    | 'inDateRange'
+    | 'notInDateRange'
+    | 'beforeDate'
+    | 'afterDate';
+
+
 
   type TimeDimensionGranularity = 'hour' | 'day' | 'week' | 'month' | 'year';