Added completion and reference for module names in config.php with tests

[drpayyne]

Description

• Added completion and reference to modules names under the modules array in config.php
• Added postive/negatives tests for the above
• Added new test assertion assertHasNoReferenceToDirectory
• Moved common logic from completion/xml/CompletionXmlFixtureTestCase.java to completion/BaseCompletionTestCase.java to make it extensible and cleaned up code wherever possible

Fixed Issues

• Fixes Add module names completion and reference in config.php #321: Add module names completion and reference in config.php

Questions

• The same ElementPattern does not work for both completion and reference. Reference seems to work only when using psiElement(StringLiteralExpression.class) and completion seems to work only when using the child of the previously mentioned element, psiElement(PhpTokenTypes.STRING_LITERAL_SINGLE_QUOTE). Is there a better way to make this common?

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
Thank you for the relly helpful functionality which makes our work more comfortable. Great 👍