extension: Fix locally unresolved defaultBuildTask

Using a complex VS Code/Codium workspace locally, upon launching Run
Extension for debugging or plain running, this removes the manual prompt
previously described in #13.

So, rather than relying on defaultBuildTask as preLaunchTask, explicitly
(directly) define the latter as the hereby expected build task. This
fixes the issue in the local case of using a complex workspace; i.e.,
made of many project folders holding such isDefault task definitions.

Fixes #13.

Signed-off-by: Marco Miller <marco.miller@ericsson.com>

Author: marco-miller

.vscode/launch.json

@@ -12,7 +12,7 @@
             "request": "launch",
             "args": ["--extensionDevelopmentPath=${workspaceFolder}"],
             "outFiles": ["${workspaceFolder}/dist/**/*.js"],
-            "preLaunchTask": "${defaultBuildTask}"
+            "preLaunchTask": "npm: watch"
         },
         {
             "name": "Extension Tests",