Speed up launching extension from VSCode debugging panel and other launch.json changes

[lilleyse]

I made a few tweaks to launch.json

• Disabled symbol loading for everything except libcesium.omniverse.plugin.so. This improves start time from 70 seconds to 15 seconds on Linux.
  • The one exception is Development App (Kit Debug) where we still include all symbols
  • This required switching to cppdgb and using symbolLoadInfo
  • No change for Windows, which was already fast enough
• Removed a few configurations
  • Performance Tracing - I'm concerned the VSCode debugger may affect performance numbers even when running release builds, so this configuration has been removed and should be run on the command line instead
  • Performance Testing App - same as above
  • C++ Unit Tests - these will eventually be folded into the tests extension, in the meantime they can still be run on the command line
  • Tests Extension - requires Ensure main extension starts before tests extension in launch configuration #470 to be fixed first
• Switched back to using VSCode integrated terminal. The original reason for switching to an external terminal is no longer applicable: Change launch.json files to use external terminal #371.