(core) Fixing bug with first click on windows

Summary:
On Windows, last row is selected when a user clicks the 'new row'
while browser doesn't have focus.

Test Plan: manual tests

Reviewers: georgegevoian

Reviewed By: georgegevoian

Subscribers: georgegevoian

Differential Revision: https://phab.getgrist.com/D3503

app/client/lib/browserInfo.ts

@@ -26,3 +26,8 @@ export function isIOS() {
 export function modKeyProp(): 'metaKey'|'ctrlKey' {
   return /Mac|iPod|iPhone|iPad/.test(navigator.platform) ? 'metaKey' : 'ctrlKey';
 }
+
+export function isWin() {
+  const os = getParser().getOSName();
+  return os === 'Windows';
+}