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

[rodrigoprimo]

Description

This PR fixes syntax errors in the XML doc code examples.

One of the invalid examples was removed because, besides containing a syntax error, it doesn't trigger the sniff (yieldfrom is tokenized as T_STRING, and this token is not watched by the sniff). The <code> title was updated to reflect the remaining examples.

Suggested changelog entry

Generic.WhiteSpace.LanguageConstructSpacing: 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.

[jrfnl]

Thanks for finding this @rodrigoprimo ! LGTM.