(core) Implement UI for trigger formulas.

Summary:
- Implement UI with "Apply to new records" and "Apply on record changes"
  checkboxes, and options for selecting which changes to recalculate on.
- For consistency, always represent empty RefList as None
- Fix up generated SchemaTypes to remember that values are encoded.

Included test cases for the main planned use cases:
- Auto-filled UUID column
- Data cleaning
- NOW() formula for record's last-updated timestamp.
- Updates that depend on other columns.

Test Plan: Added a browser test.

Reviewers: jarek

Reviewed By: jarek

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D2885

app/common/gristTypes.ts

@@ -226,6 +226,17 @@ export function getGristType(pureType: string): string {
   }
 }
 
+/**
+ * Enum for values of columns' recalcWhen property, corresponding to Python definitions in
+ * schema.py.
+ */
+export enum RecalcWhen {
+  DEFAULT = 0,         // Calculate on new records or when any field in recalcDeps changes.
+  NEVER = 1,           // Don't calculate automatically (but user can trigger manually)
+  MANUAL_UPDATES = 2,  // Calculate on new records and on manual updates to any data field.
+}
+
+
 /**
  * Converts SQL type strings produced by the Sequelize library into its corresponding
  * Grist type. The list of types is based on an analysis of SQL type string outputs

app/common/schema.ts

@@ -31,7 +31,7 @@ export const schema = {
     summarySourceCol    : "Ref:_grist_Tables_column",
     displayCol          : "Ref:_grist_Tables_column",
     visibleCol          : "Ref:_grist_Tables_column",
-    recalcWhen          : "Text",
+    recalcWhen          : "Int",
     recalcDeps          : "RefList:_grist_Tables_column",
   },
 
@@ -204,8 +204,8 @@ export interface SchemaTypes {
     summarySourceCol: number;
     displayCol: number;
     visibleCol: number;
-    recalcWhen: string;
-    recalcDeps: number[];
+    recalcWhen: number;
+    recalcDeps: ['L', ...number[]]|null;
   };
 
   "_grist_Imports": {