[NFC] Fix capitalization of class names

[braders]

Overview

Fix capitalization of class names.

This updates the dozen instances across CiviCRM core where classes were being used with different capitalisation than is used where the class is defined.

Technical Details

Whilst classes are case-insensitive in PHP I still think this makes sense:

• Consistency is good,
• Can avoid confusing if doing a search with case-sensitivity turned on,
• Avoid warnings in certain static analysis tools

[civibot]

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[braders]

Jenkins, test this please