This patch:
- Adds 3 new host platform types:
* `generic-linux` and `generic-linux-arm64` for the unsupported
linux distributions
* `<unknown>` for non-supported OS versions
- Prints a warning when downloading Ubuntu browser builds on
unsupported Linux distribution
- Makes sure launch doctor prints all missing shared libraries
on unknown Linux distributions
- Also prints an `apt` command as an alternative to Playwright CLI
dependency installation.
This patch:
- consolidates all distribution-specific information in a single
location
- updates list of required dependencies for WebKit on Arb64 Ubuntu 20.04
