pact_ffi library targeting ffi branch for beta use by users

[YOU54F]

This is a continuation of the awesome work done by @tienvx

Should hopefully contain all of your merge commits from the FFI PR's described in #262

Additional changes include

• Inclusion of testing of arm64 linux/macos
• Addition of aarch64 detection for linux/macos pact-stub-server
• Added some developer docs
• Updated readme and migration guide to for ffi to target 10.x
• Possibly borked some merge conflicts
  • I assume cores, and health check delays aren't required in the pact ffi version, as they were removed from your code.

Nice work @tienvx - Looking forward to getting this merged into the ffi branch for users to test out, and provide feedback.

I've found some php repos in the wild, so going to see if I can spend some time getting them running, and then update them to use this version, and it will provide a nice delta.

@tienvx Happy if you'd prefer to provide a singular pull request rebased against the ffi branch and I can close this off - just had some time and this was helpful to me to review all the pieces in situ

[YOU54F]

I've pushed these changes up to ffi-next on the pact-foundation branch to test out the delta between 9.x -> 10.x on the verifier side

https://github.com/YOU54F/simple-pact/pull/1/files

"pact-foundation/pact-php": "dev-ffi-next as 10.0.0"

Couple of minor snags so far

1. If no source is added, the verifier exits with a code of 0, ie if none of the following is added. This is probably sub-optimal and the user should be told they need to at least one source

   $verifier
      ->addFile('C:\SomePath\consumer-provider.json');
      ->addDirectory('C:\OtherPath');
      ->addUrl($url);
      ->addBroker($broker);

2. The upgrade guide needs a few minor tweaks, these could be coupled with some additional examples so there is some tested source paths.

Still to test out the consumer side but looking awesome and so quick!

[YOU54F]

• updated guide
• used your all branch for changes
• merged into ffi
• master merged into ffi
• then added changes to support testing in CI and stub-server for arm64

Tested out the pact-plugins

• CSV spot on
• Protobuf - consumer tests passed, provider verification passed but plugin fails to shutdown, that was on my work macbook so need to retest but that won't hold this up as they are part of separate packages