(core) Fix date filter for DateTime columns.

Summary:
Date filter was not taking timezone correclty into account, which was
causing to wrong-inclusion and wrong-exclusion of dates near the
bounds.

Diff fixes that, it also bring little refactoring that hopefully clarifies things a little.

Test Plan: Includes brand new test for `app/common/ColumnFilterFunc`.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3763

test/common/ColumnFilterFunc.ts

@@ -0,0 +1,44 @@
+import { makeFilterFunc } from "app/common/ColumnFilterFunc";
+import { FilterState } from "app/common/FilterState";
+import moment from "moment-timezone";
+import { assert } from 'chai';
+
+const format = "YYYY-MM-DD HH:mm:ss";
+const timezone = 'Europe/Paris';
+const parseDateTime = (dateStr: string) => moment.tz(dateStr, format, true, timezone).valueOf() / 1000;
+const columnType = `DateTime:${timezone}`;
+
+describe('ColumnFilterFunc', function() {
+
+
+  [
+    {date: '2023-01-01 23:59:59', expected: false},
+    {date: '2023-01-02 00:00:00', expected: true},
+    {date: '2023-01-02 00:00:01', expected: true},
+    {date: '2023-01-02 01:00:01', expected: true},
+  ].forEach(({date, expected}) => {
+
+    const minStr = '2023-01-02';
+    const state: FilterState = { min: moment.utc(minStr).valueOf() / 1000 };
+    const filterFunc = makeFilterFunc(state, columnType);
+
+    it(`${minStr} <= ${date} should be ${expected}`, function() {
+      assert.equal(filterFunc(parseDateTime(date)), expected);
+    });
+  });
+
+  [
+    {date: '2023-01-11 00:00:00', expected: true},
+    {date: '2023-01-11 23:59:59', expected: true},
+    {date: '2023-01-12 00:00:01', expected: false},
+  ].forEach(({date, expected}) => {
+
+    const maxStr = '2023-01-11';
+    const state: FilterState = { max: moment.utc(maxStr).valueOf() / 1000 };
+    const filterFunc = makeFilterFunc(state, columnType);
+
+    it(`${maxStr} >= ${date} should be ${expected}`, function() {
+      assert.equal(filterFunc(parseDateTime(date)), expected);
+    });
+  });
+});