Generic/OpeningFunctionBraceBsdAllman: improve XML documentation

[rodrigoprimo]

Description

Generic/OpeningFunctionBraceBsdAllman: fix syntax errors in the XML doc code examples

Generic/OpeningFunctionBraceBsdAllman: improve XML doc

• <documentation> title matches the sniff name.
• Mention in the <standard> description that there must be no content on the line after the opening brace and make some other minor adjustments to the description text.
• Improve the title of the <code> blocks.

Suggested changelog entry

Generic.Functions.OpeningFunctionBraceBsdAllman: minor fixes and improvements to the XML documentation

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
  • This change is only breaking for integrators, not for external standards or end-users.
• Documentation improvement

PR checklist

• I have checked there is no other PR open for the same change.
• I have read the Contribution Guidelines.
• I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• I have added tests to cover my changes.
• I have verified that the code complies with the projects coding standards.
• [Required for new sniffs] I have added XML documentation for the sniff.

[rodrigoprimo]

The remark error seems unrelated to the changes in this PR: https://github.com/PHPCSStandards/PHP_CodeSniffer/actions/runs/14359341840/job/40256467629?pr=953

[jrfnl]

The remark error seems unrelated to the changes in this PR

Should be fixed via #954 (once merged)

[jrfnl]

Thanks @rodrigoprimo !