Support PHP 8.0

[deguif]

Done in this PR:

• Update composer constraint to allow PHP 8.0.
• Update travis configuration in order to run tests on PHP 8.0 (nightly).
• Update changelog

Done in previous PRs:

• Deprecate Elastica\Query\Match class and add a new Elastica\Query\MatchQuery class as match is now a reserved keyword. [[PHP 8.0] Deprecate Match query class and introduce MatchQuery #1799]
• Update phpunit version in order to be compatible with PHP 8.0. [[PHP 8.0] Allow PHPUnit 9.4 #1811]
• Bump aws/aws-sdk-php package version to fix a bug with PHP 8.0. [[PHP 8.0] Use AWS SDK package version compatible #1798]

Done in external PRs:

• Wait for aws/aws-sdk-php to be compatible with PHP 8. [https://github.com/Fixed crash on PHP 8.0 aws/aws-sdk-php#2079]
• Wait for elasticsearch/elasticsearch to be compatible with PHP 8.0 and remove --ignore-platform-reqs composer option.

[deguif]

One failure is remaining on PHP 8.0 but it's related to aws SDK.
See aws/aws-sdk-php#2079 for details and the fix that should be merged soon (I hope).

[ruflin]

@deguif Thanks for getting this started. We had in the past a similar issue with a naming conflict with the Bool query. What we did back then is rename it to BoolQuery instead: https://github.com/ruflin/Elastica/blob/master/src/Query/BoolQuery.php I wonder if we should follow the same pattern here instead of using the _ for consistency? MatchQuery?

[ruflin]

@deguif This will also need an update of the CHANGELOG and I wonder if we should also update the readme that it now running at least tests with PHP 8.0?

[GrahamCampbell]

Bump aws/aws-sdk-php package version to fix a bug with PHP 8.0 (aws/aws-sdk-php#2079).

There are definitely more similar bugs like the one that I fixed. Amazon's job is to fix that, though. I have just fixed the one that affected me.

[GrahamCampbell]

Also, Guzzle, a dependency of the AWS SDK is not ready for PHP 8 yet.

[ruflin]

Is there option to exclude the AWS part for 8.0 for now?

[GrahamCampbell]

Guzzle is now ready, btw. 7.2.0 supports PHP 8.0.

[deguif]

Since PHP 8.0 RC1 a 0 port number is considered valid: See php/php-src#6152
For details see how it behaves on other PHP versions: https://3v4l.org/ZYhJc

[deguif]

@ruflin I think this PR is now ready.
Testing on PHP 8.0 is now green with all the changes done in previous PRs.

I will later update the PHP version in travis configuration to 8.0 and also remove the composer flag --ignore-platform-reqs when elasticsearch/elasticsearch will officially support PHP 8.0.

[ruflin]

@deguif Nice! Thank you!