Add file name handler support for 'make-process' (Bug#28691)

Add file name handler support for 'make-process' (Bug#28691)

* src/process.c (Fmake_process): Add new keyword argument
':file-handler'.
(syms_of_process) <make-process, :file-handler>: Define new symbols.

* lisp/files.el (file-name-non-special): Add support for
'make-process'.

* test/src/process-tests.el (make-process/file-handler/found)
(make-process/file-handler/not-found)
(make-process/file-handler/disable): New unit tests.
(process-tests--file-handler): New helper function.

* test/lisp/files-tests.el
(files-tests-file-name-non-special-make-process): New unit test.

* doc/lispref/files.texi (Magic File Names): Document that
'make-process' can invoke file name handlers.

* doc/lispref/processes.texi (Asynchronous Processes): Document
':file-handlers' argument to 'make-process'.

* etc/NEWS (Lisp Changes in Emacs 27.1): Mention new
:file-handler argument for 'make-process'.