Add --vscode-launch-file to gdbclient.py

The new argument makes the generator write the VSCode launch.json config
into a file instead of stdout.

The generator uses marker lines to insert the config. This way the user
can control where in the file the launch config is written.

Test: atest gdbclient_test
Test: lldbclient.py --setup-forwarding vscode-lldb \
  --vscode-launch-props= \
  '{"internalConsoleOptions" : "openOnSessionStart"}' \
  --vscode-launch-file=.vscode/launch.json -r test

Change-Id: I92b3f479b5ebcb722933938f52d0f23ff098beac
2 files changed