Flesh out required and suggested extensions in composer.json based on Hosting handbook

[westonruter]

Trac ticket: https://core.trac.wordpress.org/ticket/65571

See https://make.wordpress.org/hosting/handbook/server-environment/#required-extensions

Notes:

• All PHP extensions, whether highly recommended or merely suggested by the handbook, are all included in suggest.
• The mysqli extension is moved from suggest to require.
• The hash extension is only suggested by the Handbook page but it is actually required.
• The image extension mentioned by the Handbook page is actually the gd extension.

Use of AI Tools

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Tool(s): Claude Code
Model(s): Claude Opus 4.8
Used for: Code review

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