[web] use a different method for launching desktop safari

[yjbanov]

Replace open -F -W -n -b com.apple.Safari with a direct invocation of the /Applications/Safari.app/Contents/MacOS/Safari executable.

Problems with open:

• The open process itself is short-lived and exits immediately after launching Safari. This is contrary to the assumptions made by the rest of the code that the lifetime of the process returned by the Browser class corresponds to the browser process.
• The Safari process is left open after the test is finished.
• The open command and/or com.apple.Safari also open the "default browser". For example, if your default browser is set to Chrome, then the test will also open in Chrome.

The method used here is borrowed from Karma: karma-runner/karma-safari-launcher#29

This also removes the "clear console" functionality when felt is run in normal mode (as opposed to watch mode), which could be messing with LUCI logs.

This also removes the printouts of macOS info, because commands we use to extract this info are flaky.

Fixes flutter/flutter#86676

[flutter-dashboard]

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[yjbanov]

Merging on red LUCI to fix the build.