PHP version update

[Shikachuu]

Signed-off-by: Shikachuu zcmate@gmail.com

Description

To mostly maintain backward compatibility I update the images to PHP 7.4 to keep the php7 name.
Update PHP version everywhere to 7.4, changed composer flag to :1 to always use the most up-to-date composer:1 version.
(I also added type hints to the Handler class, but that's not the main topic of this pull request, so it can be removed if there is a need.)

Motivation and Context

The reason behind this PR is that PHP 7.2 is EOL since 2020 November and composer was way down in security patches.

• I have raised an issue to propose this change (required) PHP version update #267

Which issue(s) this PR fixes

How Has This Been Tested?

Since it is just a version bump in the Dockerfile I just ran a Docker build command to check for complications.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Version change (see: Impact to existing users)

Impact to existing users

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.

[alexellis]

Before you made this explicitly into a string, what kind of data was being passed in here?

[Shikachuu]

It was/is string, it gets data directly from file_get_contents("php://stdin"), which is read the entire stdin into a string or return false on failure (in case of an explicit php://stdin should never happen).
https://www.php.net/manual/en/function.file-get-contents

The explicit string type is only there to aid the developer, nothing fancy.

[alexellis]

Thanks for clarifying.

[alexellis]

LGTM