(core) Allow filtering by selected cell value in cell context menu

Summary: Adds a command and `BaseView` method `filterByThisCellValue`.

Test Plan: Added two tests to `nbrowser/CellContextMenu.ts`

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3383

app/client/components/BaseView.js

@@ -229,6 +229,8 @@ BaseView.commonCommands = {
   insertCurrentDateTime: function() { this.insertCurrentDate(true); },
 
   copyLink: function() { this.copyLink().catch(reportError); },
+
+  filterByThisCellValue: function() { this.filterByThisCellValue(); },
 };
 
 /**
@@ -305,6 +307,26 @@ BaseView.prototype.copyLink = async function() {
   }
 };
 
+BaseView.prototype.filterByThisCellValue = function() {
+  const rowId = this.viewData.getRowId(this.cursor.rowIndex());
+  const col = this.viewSection.viewFields().peek()[this.cursor.fieldIndex()].column();
+  let value = this.tableModel.tableData.getValue(rowId, col.colId.peek());
+
+  // This mimics the logic in ColumnFilterMenu.addCountsToMap
+  // ChoiceList and Reflist values get 'flattened' out so we filter by each element within.
+  // In any other column type, complex values (even lists) get converted to JSON.
+  let filterValues;
+  if (gristTypes.isList(value) && gristTypes.isListType(col.type.peek())) {
+    filterValues = value.slice(1);
+  } else {
+    if (Array.isArray(value)) {
+      value = JSON.stringify(value);
+    }
+    filterValues = [value];
+  }
+  this.viewSection.setFilter(col.getRowId(), JSON.stringify({included: filterValues}));
+};
+
 /**
  * Insert a new row immediately before the row at the given index if given an Integer. Otherwise
  * insert a new row at the end.

app/client/components/commandList.js

@@ -384,6 +384,15 @@ exports.groups = [{
     },
 
   ],
+}, {
+  group: 'Filtering',
+  commands: [
+    {
+      name: 'filterByThisCellValue',
+      keys: [],
+      desc: `Filter this column by just this cell's value`,
+    },
+  ]
 }, {
   group: 'Linking',
   commands: [