Add Tramp support of direct asynchronous process invocation

Add Tramp support of direct asynchronous process invocation

* doc/misc/tramp.texi (Predefined connection information):
Add "direct-async-process".
(Remote processes): New subsection "Improving performance of
asynchronous remote processes".

* lisp/net/tramp-adb.el (tramp-methods) <adb>: Add `tramp-login-program'
and `tramp-login-args'.
(tramp-adb-handle-make-process): Use `tramp-handle-make-process'.
(tramp-adb-maybe-open-connection): Add "set +o vi +o emacs" command.

* lisp/net/tramp-sh.el (tramp-sh-handle-make-process):
Use `tramp-handle-make-process'.
(tramp-sh-file-name-handler-p, tramp-multi-hop-p): New defuns.
(tramp-compute-multi-hops): Use `tramp-multi-hop-p'.

* lisp/net/tramp.el (tramp-dissect-file-name, tramp-dissect-hop-name):
Use `tramp-multi-hop-p'.
(tramp-handle-insert-file-contents, tramp-local-host-p):
Use `tramp-sh-file-name-handler-p'.
(tramp-handle-make-process): New defun.

* test/README: Add another example how to use SELECTOR.

* test/lisp/net/tramp-tests.el (tramp-test03-file-name-method-rules):
Adapt test.
(tramp--test-sh-p): Use `tramp-sh-file-name-handler-p'.