(core) Fix scrolling and column title bugs

Summary:
On Firefox and Safari, setting scrollLeft to a max safe integer was
causing it to be treated as 0. It's not clear why - for now, the
scrollWidth is used instead.

Also fixes a bug where the column title popup wouldn't appear for a
new column if tab was previously used to close the same popup for
the last column.

Test Plan: Browser test.

Reviewers: JakubSerafin

Reviewed By: JakubSerafin

Subscribers: dsagal

Differential Revision: https://phab.getgrist.com/D3911

test/nbrowser/DescriptionColumn.ts

@@ -364,6 +364,23 @@ describe('DescriptionColumn', function() {
     await revert();
   });
 
+  it('should reopen editor when adding new column', async () => {
+    // This partially worked before - there was a bug where if you pressed tab on
+    // the last column, and then clicked Add Column, the editor wasn't shown, and the
+    // auto-generated column name was used.
+    const revert = await gu.begin();
+    await doubleClickHeader('E');
+    await gu.sendKeys(Key.TAB);
+    assert.isFalse(await popupVisible());
+
+    await addColumn();
+    assert.isTrue(await popupVisible());
+
+    await gu.sendKeys(Key.ESCAPE);
+    await gu.waitForServer();
+    await revert();
+  });
+
   it('should support basic edition on CardList', async () => {
     const mainSession = await gu.session().teamSite.login();
     const api = mainSession.createHomeApi();