Unify cache configuration

[sebastianbergmann]

A phpunit.xml configuration file that uses best practice defaults (as generated using --generate-configuration) for PHPUnit 9.5 looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd"
         bootstrap="vendor/autoload.php"
         cacheResultFile=".phpunit.cache/test-results"
         executionOrder="depends,defects"
         forceCoversAnnotation="true"
         beStrictAboutCoversAnnotation="true"
         beStrictAboutOutputDuringTests="true"
         beStrictAboutTodoAnnotatedTests="true"
         failOnRisky="true"
         failOnWarning="true"
         verbose="true">
    <testsuites>
        <testsuite name="default">
            <directory suffix="Test.php">tests</directory>
        </testsuite>
    </testsuites>

    <coverage cacheDirectory=".phpunit.cache/code-coverage"
              processUncoveredFiles="true">
        <include>
            <directory suffix=".php">src</directory>
        </include>
    </coverage>
</phpunit>

The cacheResultFile attribute of the <phpunit> root element (as well as the --cache-result-file <file> CLI option) is used to configure the file where the PHPUnit test runner stores its test result cache.

The cacheDirectory attribute of the <coverage> element (as well as the --coverage-cache <dir> CLI option) is used to configure the directory where static analysis results for code coverage are cached.

In the future, there will be more "things" we would like to cache. I therefore propose the following:

• Deprecate the cacheResultFile attribute of the <phpunit> root element (as well as the --cache-result-file <file> CLI option) in PHPUnit 10 (and remove support for it in PHPUnit 11)
• Deprecate the cacheDirectory attribute of the <coverage> element (as well as the --coverage-cache <dir> CLI option) in PHPUnit 10 (and remove support for it in PHPUnit 11)
• Introduce the cacheDirectory attribute on the <phpunit> root element (as well as the --cache-directory <dir> CLI option) for configuring a single root directory for cache directories and cache files used by the PHPUnit test runner in PHPUnit 10
• Change --generate-configuration to generate the following

<?xml version="1.0" encoding="UTF-8"?>
<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.0/phpunit.xsd"
         bootstrap="vendor/autoload.php"
         cacheDirectory=".phpunit.cache"
         executionOrder="depends,defects"
         forceCoversAnnotation="true"
         beStrictAboutCoversAnnotation="true"
         beStrictAboutOutputDuringTests="true"
         beStrictAboutTodoAnnotatedTests="true"
         failOnRisky="true"
         failOnWarning="true"
         verbose="true">
    <testsuites>
        <testsuite name="default">
            <directory suffix="Test.php">tests</directory>
        </testsuite>
    </testsuites>

    <coverage processUncoveredFiles="true">
        <include>
            <directory suffix=".php">src</directory>
        </include>
    </coverage>
</phpunit>