Squiz/FunctionOpeningBraceSpace: update XML doc

[rodrigoprimo]

Description

This PR updates the XML documentation of the Squiz.WhiteSpace.FunctionOpeningBraceSpace sniff to address the following:

• Update the sniff description and remove a code example for something that the sniff doesn't check. The sniff only checks for blank lines after the opening brace of a function, and not if the opening brace is on its own line.
• Ensure the title matches the sniff name.

Suggested changelog entry

Squiz.WhiteSpace.FunctionOpeningBraceSpace: 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.

[jrfnl]

Thanks @rodrigoprimo !

For the record: there did use to be a "opening brace on same line/new line" check for JS. This was removed in 34543c8.