Handle invocations like cvd -h or cvd --help

Treating it at `cvd help` uses existing logic, rather than trying to
force the handling into selectors parsing or handle it as a "driver"
flag (how `verbosity` is handled in `main`).

The selector flags are already processed by this point and do not
interfere.

Bug: 387539609
Test: cvd -h
Test: cvd --help
Test: cvd -help version
Test: cvd --instance_name=test -h
Test: cvd --selector_typo=test -h

base/cvd/cuttlefish/host/commands/cvd/cli/command_request.cpp

@@ -20,6 +20,7 @@
 #include <vector>
 
 #include "common/libs/utils/files.h"
+#include "common/libs/utils/flag_parser.h"
 #include "common/libs/utils/result.h"
 #include "host/commands/cvd/cli/command_request.h"
 #include "host/commands/cvd/cli/selector/selector_common_parser.h"
@@ -44,6 +45,12 @@ CommandRequest::CommandRequest(cvd_common::Args args, cvd_common::Envs env,
     subcommand_ = subcommand_arguments_[0];
     subcommand_arguments_.erase(subcommand_arguments_.begin());
   }
+
+  //  transform `cvd -h` or `cvd --help` requests into `cvd help`
+  Result<bool> is_top_level_help_flag = HasHelpFlag({subcommand_});
+  if (is_top_level_help_flag.ok() && *is_top_level_help_flag) {
+    subcommand_ = "help";
+  }
 }
 
 CommandRequestBuilder& CommandRequestBuilder::AddArguments(