New package pattern.0.1.0 (#14146)
* New package pattern.0.1.0
pattern is a PPX extension that generates functions from patterns
that explain match failures by returning the common context and the
list of differences between a pattern and a value.
* Add build instruction!
* Remove reference to ppx_deriving
* Add ppx_deriving to dependencies
* Update dependencies in the ocaml repo
* Fix compatibility with old OCaml versions
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