devtool: ide: vscode: Configure read-only files

devtool: ide: vscode: Configure read-only files

When debugging or browsing files, the user may fall into external
sources from other packages in the sysroot or dbg-rootfs. Modifying them
will only lead to confusion since they will be overwritten by Yocto. The
user should open them in a separate devtool modify session if they want
to make changes. Meanwhile, we should prevent write access to them.

Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@savoirfairelinux.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>