(core) On mobile, only show a warning for older and unknown browsers rather than for all

Test Plan:
Tested listed versions against docs.getgrist.com using browserstack, and tested
with an iPhone and local server that new settings are noticed on mobile.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3909

app/client/browserCheck.ts

@@ -20,7 +20,14 @@ if (document && window && document.cookie.indexOf("gristbrowser=accept") === -1)
       safari: ">=12.0.3",      // first 2019 version
       edge: ">=80",            // one of first Chromium-based Edge versions, early 2020
       opera: ">=66",           // first 2020 version
-    }
+    },
+    mobile: {
+      // These were tested using browserstack, for a basic layout and cell editing. Other browsers
+      // not attempted, so Grist will show a warning there.
+      safari: ">=15",       // 2021 version, first where layouts aren't broken
+      chrome: ">=92",       // 2021 version which works fine
+      firefox: ">=108",     // end-of-2022 version, couldn't try an earlier one
+    },
   });
   const isMobile = version.isPlatform('mobile') || version.isPlatform('tablet');
   if (!isHappyBrowser) {

static/app.html

@@ -49,7 +49,7 @@
           Grist works best on modern Firefox or Chrome.
         </span>
         <span class="browser-check-mobile">
-          Grist mobile support is a work in progress.
+          Grist mobile works best on modern Firefox, Chrome, or Safari.
         </span>
         <a href="https://support.getgrist.com/browser-support" target="_blank">Learn more</a>
       </td>