Replace —print-build-dir with --dump-config

The --dump-config option prints a recursive JSON dump of the BuildScriptInvocation object’s properties, which gives access to essentially all of the knowledge build-script has about the build before it starts performing it. This makes the output more flexible and extensible without severely convoluting the implementation, but doesn’t really give us a stable representation of that data.

utils/build_swift/driver_arguments.py

@@ -287,6 +287,10 @@ def create_argument_parser():
     option(['-n', '--dry-run'], store_true,
            help='print the commands that would be executed, but do not '
                 'execute them')
+    option('--dump-config', toggle_true,
+           help='instead of building, write JSON to stdout containing '
+                'various values used to build in this configuration')
+
     option('--legacy-impl', store_true('legacy_impl'),
            help='use legacy implementation')
 
@@ -333,8 +337,6 @@ def create_argument_parser():
            metavar='PATH',
            help='name of the directory under $SWIFT_BUILD_ROOT where the '
                 'build products will be placed')
-    option('--print-build-dir', toggle_true,
-           help='print the build directory and exit without building')
     option('--install-prefix', store_path,
            default=targets.install_prefix(),
            help='The installation prefix. This is where built Swift products '