Fix help for completion_metrics

As it is, it is broken if you pass `--help`.

Also, this adds line wrapping for option help text.

Change-Id: Ia1e096eba46b1f4db804f9c1ed771d4e67816ae8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/242020
Auto-Submit: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/tool/code_completion/completion_metrics.dart

@@ -151,8 +151,9 @@ Counter rankComparison = Counter('relevance rank comparison');
 
 /// Create a parser that can be used to parse the command-line arguments.
 ArgParser createArgParser() {
-  return ArgParser()
-    ..addOption(
+  return ArgParser(
+      usageLineLength: stdout.hasTerminal ? stdout.terminalColumns : 80)
+    ..addFlag(
       'help',
       abbr: 'h',
       help: 'Print this help message.',