Automatically generate launch.json

[mjp41]

This adds a CMake option to automatically generate the launch.json file for vscode that runs everything in the testsuite.

This generates a launch.json like:

{
  "version": "0.2.0",
  "configurations": [
        {
      "name": "verona/basic/ex1",
      "type": "cppdbg",
      "request": "launch",
      "program": "/home/mjp41/verona/build/dist/verona/verona",
      "args": ["build", "ex1.verona", "-w", "-o", "/home/mjp41/verona/build/testsuite/verona/basic/ex1_out/ast"],
      "stopAtEntry": false,
      "cwd": "/home/mjp41/verona/testsuite/verona/basic",
    },
    {
      "name": "verona_nostdlib/basic/ex1",
      "type": "cppdbg",
      "request": "launch",
      "program": "/home/mjp41/verona/build/dist/verona/verona",
      "args": ["build", "ex1.verona", "-w", "-o", "/home/mjp41/verona/build/testsuite/verona_nostdlib/basic/ex1_out/ast", "--dump_passes", "/home/mjp41/verona/build/testsuite/verona_nostdlib/basic/ex1_out", "--no-std", "-p", "defaultargs"],
      "stopAtEntry": false,
      "cwd": "/home/mjp41/verona/testsuite/verona_nostdlib/basic",
    },
    {
      "name": "verona_nostdlib/spec/comments",
      "type": "cppdbg",
      "request": "launch",
      "program": "/home/mjp41/verona/build/dist/verona/verona",
      "args": ["build", "comments.verona", "-w", "-o", "/home/mjp41/verona/build/testsuite/verona_nostdlib/spec/comments_out/ast", "--dump_passes", "/home/mjp41/verona/build/testsuite/verona_nostdlib/spec/comments_out", "--no-std", "-p", "defaultargs"],
      "stopAtEntry": false,
      "cwd": "/home/mjp41/verona/testsuite/verona_nostdlib/spec",
    },
    {
      "name": "verona_nostdlib/spec/comments_broken_nest",
      "type": "cppdbg",
      "request": "launch",
      "program": "/home/mjp41/verona/build/dist/verona/verona",
      "args": ["build", "comments_broken_nest.verona", "-w", "-o", "/home/mjp41/verona/build/testsuite/verona_nostdlib/spec/comments_broken_nest_out/ast", "--dump_passes", "/home/mjp41/verona/build/testsuite/verona_nostdlib/spec/comments_broken_nest_out", "--no-std", "-p", "defaultargs"],
      "stopAtEntry": false,
      "cwd": "/home/mjp41/verona/testsuite/verona_nostdlib/spec",
    },
  ]
}

You need to run

cmake -DVERONA_GENERATE_LAUNCH_JSON=On ..

and it will write to that location with a launch.json that contains all the tests from the testsuite.