Add support for LG WebOS

[joeyparrish]

Basic docs on building a web app for WebOS:

• https://webostv.developer.lge.com/sdk/installation/
• https://webostv.developer.lge.com/sdk/tools/using-webos-tv-cli/
• https://webostv.developer.lge.com/develop/building-your-first-web-app-webos-tv/

This could work very similarly to the Tizen backend:

• https://github.com/google/generic-webdriver-server/blob/main/backends/tizen/README.md
• https://github.com/google/generic-webdriver-server/blob/main/backends/tizen/how-it-works.md

[joeyparrish]

See also https://github.com/google/shaka-player/issues/1330#issuecomment-384092100