[Forwardport] Avoid undefined index warning when using uppercase reserved word

[FreekVandeursen]

Original Pull Request

#16785
ReservedWordsSniff will trigger an undefined index error if a reserved word is used in uppercase.

Manual testing scenarios

1. Create a class containing a reserved word, with at least 1 uppercase character (e.g. Bool)
2. execute phpcs codesniffer with dev/tests/static/framework/Magento/ruleset.xml ruleset

Expected result

Code sniffer error "Cannot use "Bool" in namespace as it is reserved since PHP 7"

Actual result

Code sniffer error "An error occurred during processing; checking has been aborted. The error message was: Undefined index: Bool"

[magento-engcom-team]

Hi @FreekVandeursen. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

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[magento-engcom-team]

Hi @FreekVandeursen. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.