fix(windows): hide console window when launching headless browsers

[triemerge]

Rationale

The tricky part here is that launchProcess() is shared by all browser launches, including headed ones like codegen and Inspector. Setting windowsHide unconditionally would hide those too, so it needs to be opt-in and only kick in for headless launches.

While at it, also applied it to the ffmpeg and taskkill spawns since neither of those should be showing a console window either.

Fixes #41630

[yury-s]

How do we ensure it does not introduce the same regression that required reverting previous fix in #39994 ?

[triemerge]

How do we ensure it does not introduce the same regression that required reverting previous fix in #39994 ?

The previous fix just set it unconditionally inside launchProcess so headed stuff like codegen and UI mode got caught in it too. This time around it's opt-in, so only headless launches actually get the flag. Headed ones don't get it at all since options.headless is false for them, so there's no change in behavior there.