Support environment variables in browser desktop files

[jelenv]

The launch scripts omarchy-launch-browser and omarchy-launch-webapp now extract and forward env variables in browser desktop files correctly.

Fixes launching Chrome with custom hardware acceleration flags and similar configurations.

For example this configuration in google-chrome.desktop file now correctly works:

Exec=env LIBVA_DRIVER_NAME=radeonsi /usr/bin/google-chrome-stable --disable-features=WaylandWpColorManagerV1 %U

This is often needed on hybrid GPU laptops.