Add feature for app install API

[ddbeck]

Specification

• https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/WebInstall/explainer.md
• Add navigator.install() w3c/manifest#1175

Description

Discovered via #3399 and Chromium use counters, so I don't actually know a lot about this. Here's my educated guess:

The navigator.install() method triggers the installation a progressive web app.

Documentation

• https://kbhlee2121.github.io/pwa/web-install/index.html

Browser support

• https://chromestatus.com/feature/5183481574850560