Changed validator for CreateAnObserverDialog

[drpayyne]

Description

Changed validator for com.magento.idea.magento2plugin.actions.generation.dialog.CreateAnObserverDialog. Also fixed PhpClassRule's edge case bug where providing a PHP reserved keyword breaks the code.

Fixed Issues

1. Change validation for Creating new observer dialog window #283: Change validation for Creating new observer dialog window

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with integration/functional tests (if applicable)
• All automated tests passed successfully (all builds are green)

[coderimus]

Hello @drpayyne
Everything great and I approved this PR. Please, create a backport for the "Also fixed PhpClassRule's edge case bug where providing a PHP reserved keyword breaks the code." to the 2.0.1
Thank you!

[coderimus]

@drpayyne please, ignore my comment about the backport. Here we do not need it, I was wrong. Thank you!