vscode updates and improvements

- fix gazebo SITL debug
     - now prompts you to select vehicle
 - devcontainer.json container support https://code.visualstudio.com/docs/remote/containers
     - this allows you to jump straight into working within a container (px4-dev-nuttx) on a fresh machine
     - also helps with Codespaces https://github.com/features/codespaces
 - plugin updates
    - cpp extension pack, spell checking, CTest support
 - cleanup intellisense
     - the backup tag parser was a resource hog and didn't work very well
 - fix problemMatcher support so that you can click on a build failure

.vscode/extensions.json

@@ -4,6 +4,7 @@
     "recommendations": [
         "chiehyu.vscode-astyle",
         "dan-c-underwood.arm",
+        "fredericbonnet.cmake-test-adapter",
         "github.vscode-pull-request-github",
         "marus25.cortex-debug",
         "ms-azuretools.vscode-docker",
@@ -11,8 +12,9 @@
         "ms-python.python",
         "ms-vscode.cmake-tools",
         "ms-vscode.cpptools",
+        "ms-vscode.cpptools-extension-pack",
         "redhat.vscode-yaml",
-        "timonwong.shellcheck",
+        "streetsidesoftware.code-spell-checker",
         "twxs.cmake",
         "uavcan.dsdl",
         "wholroyd.jinja",