Add requirement for PHP extensions to composer.json

[fredden]

WHY are these changes introduced?

On line 188 of src/Clients/Http.php, the function mb_strlen() is used. After installing this library on a new server, I got an error from PHP saying:
PHP Fatal error: Uncaught Error: Call to undefined function Shopify\Clients\mb_strlen() in .../vendor/shopify/shopify-api/src/Clients/Http.php:188

shopify-api-php/src/Clients/Http.php

Line 188 in 432676a

->withHeader(HttpHeaders::CONTENT_LENGTH, mb_strlen($bodyString));

WHAT is this pull request doing?

This pull request updates the list of requirements in composer.json to include the mbstring extension, which is required for this library to work properly.

Update: while I was completing the 'checklist' in the GitHub pull request template, I added a test to catch this problem, and found some more extensions which are required and not listed.

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above
• I have added/updated tests for this change
• I have updated the documentation for public APIs from the library (if applicable)

[wilsenhc]

LGTM! I hope we can get this merged soon

[wilsenhc]

Still LGTM, hopefully we can get this merged soon @paulomarg 🚀

[Jan0707]

Hi @fredden !

We have just recently added validation and normalization for composer.json to our workflow. Would you mind updating your PR to resolve the conflicts :)

Looks good otherwise!

[fredden]

@Jan0707 yes. I've resolved the merge conflicts introduced today twice now. Feel free to squash-merge this to keep the main branch clean, or I can rebase this onto the main branch if you'd prefer.

[Jan0707]

Looks good to me!