Support PHP 8.0; Drop 5.6, 7.0 & 7.1

[jdavid]

Add support for PHP 8.0

[QuintinWillison]

Added @kavalerov as a reviewer as he may have opinions on dropped runtime support.

[kavalerov]

I haven't tested the SDK itself, but change in supported versions looks right to me, yes.

[owenpearson]

For visibility - the change in supported versions here is in line with current PHP support

[jdavid]

To get the test suite working with PHP 8.0 we have to upgrade PHPUnit. Only versions 8 and 9 support PHP 8.0, see https://phpunit.de/supported-versions.html

Note that there are no changes to the src folder. So this version could work with PHP 5.6, 7.0 and 7.1, but the tests won't pass.

Breaking changes in PHPUnit require to update the test suite. So the tests either pass with PHP 8.0 or with the older versions, but not both.

PHP 5.6 error, see https://github.com/ably/ably-php/runs/2041202213?check_suite_focus=true

PHP Parse error:  syntax error, unexpected ':', expecting ';' or '{' in ...

PHP 7.0 error, see https://github.com/ably/ably-php/runs/2041202230?check_suite_focus=true

PHP Fatal error:  Uncaught TypeError: Return value of DebugTestListener::startTestSuite() must be an instance of void, none returned in ...

PHP 7.1 error, see https://github.com/ably/ably-php/runs/2041202249?check_suite_focus=true

PHP Fatal error:  Declaration of DebugTestListener::endTest(PHPUnit\Framework\Test $test, $time): void must be compatible with PHPUnit\Framework\TestListener::endTest(PHPUnit\Framework\Test $test, float $time): void in ...

While the commit is large, there are only a few changes that repeat through the test suite:

• Update phpunit.xml to use whitelist instead of blacklist
• Update DebugTestListener.php to use TestListenerDefaultImplementation instead of PHPUnit_Framework_BaseTestListener
• Replace \PHPUnit_Framework_TestCase by \PHPUnit\_Framework\_TestCase
• Add : void to TestCase functions. This is the change that produces the syntax error in PHP 5.6
• Replace assertContains by assertStringContainsString
• Replace assertInternalType by assertIsString
• Use $this->expectException(..) instead of @expectedException ...
• Use assertions instead of fail(...)
• Fix testIdempotentLibraryGenerated, which worked before only by accident