Multi step plugin archive

[Biont]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Refactoring

What is the current behavior? (You can also link to an open issue here)
build-plugin-archive.yml uses a single php version for bundling dependencies and executing build tools.
WP's committment to supporting php down to 7.0 makes it increasingly cumbersome to support "one" php platform requirement for production AND development/building.

We have been accepting this limitation in order to streamline our packaging across most of our projects - and it's been a very solid base. But the fact remains that the php ecosystem is moving on while the php7 support requirement for WP packages is not going anywhere. Since this gap is only getting wider, we need to find a better approach

What is the new behavior (if this is a feature change)?
The logic of the workflow has been split into 3 parts:

1. Production dependencies - checkout the repo and composer install using the ancient PHP version
2. Build steps - execute all relevant build tools using a much more modern php version. We also no longer expect these to be present in dev dependencies: If we find a config, we install the tool globally.
3. Archive creation - add final touches and create the resulting archive

Note: There is no strict technical requirement for step 3 to be in a separate job. It adds a little overhead, but I think at this point, it adds a nice separation of concerns in that it keeps a few environment variables and data handling out of the other steps.

The individual jobs each produce their own "interim" artifact which is then picked up by the next one. This makes it easy to spot and debug where something went wrong:

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This change frees us from having to use EOL versions of common tools and also paves the way for modernization of our own tools, for example dropping PHP 7 in Composer Asset Compiler. It also allows us to introduce third-party tools like php-scoper with ease since we are no longer subject to the php version constraints of individual projects.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
No

Other information:

[tyrann0us]

Thanks for incorporating the changes so quickly. LGTM. Left a minor comment that doesn't stop me from approving. 💪🏽