fix: don't destroy BrowserView webContents when owning BrowserWindow hasn't been closed (#42353)
* fix: moves bv webContents close to closed event
* chore: adds unit tests
* chore: test that bv webContents are destroyed when parent bw closed
Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Anny Yang <anny@electronjs.org>