true/false: put Usage: on the first line of --help (#10279)

[jamesarch]

Closes #10279.

Problem

GNU true --help and false --help start with the Usage: line:

$ LANG=C /usr/bin/false --help | head -1
Usage: /usr/bin/false [ignored command line arguments]

uutils put the about text first, so the first line was Returns false, an unsuccessful exit status. instead. Config tools and packaging scripts that
grep the synopsis from the first line broke. Reported in the Ubuntu
launchpad bug linked from the issue.

Fix

• Add uucore::localized_help_template_usage_first, a GNU-style ordering
  variant of the existing localized_help_template. Keeps the localized
  Usage: label and the bold + underline styling, but emits it before the
  about block.
• Switch true and false to use the new template.

Other utilities continue to use the existing template — this PR is
intentionally narrow so it doesn't churn snapshot tests elsewhere. If
maintainers want to roll the GNU-style ordering out broadly later, the
helper is already in place.

Tests

• test_help_starts_with_usage added for both true and false,
  asserting the first line of --help starts with Usage:.

$ cargo test --features 'true,false' --test tests -- test_true test_false
running 14 tests
test result: ok. 14 passed; 0 failed

🤖 Generated with Claude Code

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/follow-name (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/basenc/bounded-memory is now being skipped but was previously passing.
Congrats! The gnu test tests/cut/cut-huge-range is now passing!
Congrats! The gnu test tests/rm/many-dir-entries-vs-OOM is now passing!