Replace the isStandalone const with a method of the same name

[a-stewart]

This PR fixes #143197

Logic based on if the window is standalone should be based on if it is currently standalone, rather than if it was standalone when VS Code was started.

[bpasero]

Looks pretty cool, I was not aware that MediaQueryList offers a change event 👏

@rebornix wanna give it a second pair of eyes, given you originally added this property?

[a-stewart]

Looks like addEventListener is deprecated now in favour of onchange. I'll update

Edit: ignore me, it was addListener that was deprecated, not addEventListener

This seems to already be defined in dom.ts. Importing dom would create a circular dependency, but we could move this method into browser.ts and re-export from dom.ts if you think that would be cleaner.

[rebornix]

@a-stewart thanks for the contribution, didn't know there is an event emitter for the mode change, really nice!

[a-stewart]

@rebornix - there is a potentially cleaner way of doing it if we move the existing watcher from dom.ts into browser.ts:

https://github.com/a-stewart/vscode/compare/make-isStandalone-a-method...a-stewart:addMatchMediaChangeLIstener-in-browser-ts?expand=1

WDYT?

[bpasero]

Yeah sounds good to move that.

[a-stewart]

I've creating another PR with the handler moved to dom.ts: #143287