Disabled cookies gives misleading "Browser can't run element" error

### Description

Loading app.element.io in a browser with cookies disabled gives a misleading error message about the browser not being able to run Element, when in reality the issue may be fixed simply by enabling cookies.

(I am not familiar with the frequency with which people browse with cookies disabled, but doing so is a minimally invasive process, at least with Chrome where the interface allows you to persistently enable cookies for a site with three quick mouse clicks within an existing tab.)

### Steps to reproduce

- Start Chrome. (Version/platform information is below).
- From the Settings page, under "Privacy and Security," click "Cookies and other site data" and select the "Block all cookies" setting. (This is my default setting.) Use the search box at the upper right (not the centred search box above that) to search for "element" and ensure that app.element.io or a pattern matching it does not appear in the list of allowed sites.
- Open a new tab and navigate to https://app.element.io/ . The cookie icon at the right of the URL bar will have a red "X" in the lower corner. You will see a message saying "Unsupported browser," "Your browser can't run Element," "Element uses many advanced browser features, some of which are not available or experimental in your current browser." 
- Click the cookie icon at the right of the URL bar; in the small pop-up dialogue box select "Always allow app.element.io to set cookies," and click the button to reload the page. The error message will be replaced by the expected, working app.

### Version information

- **Platform**: Web
- **Browser**: 83.0.4103.116 (Official Build) (64-bit) (cohort: Stable)
- **OS**: " Windows 10 Pro version 1909
- **URL**: https://app.element.io/