Compile external fun expressions to literals

OTP-15003

* dgud/revert-string-depr:
  Revert "Deprecate old string functions"

The expressions fun M:F/A, when all elements are literals are also
treated as a literal. Since they have consistent representation and
don't depend on the code currently loaded in the VM, this is safe.
This can provide significant performance improvements in code using such
functions extensively - a full function call to erlang:make_fun/3 is
replaced by a single move instruction and no register shuffling or
saving registers to stack is necessary. Additionally, compound data
types that contain such external functions as elements can be treated as
literals too.

The commit also changes the representation of external funs to be a
valid Erlang syntax and adds support for literal external funs to core
Erlang.

* raimo/type-posix-0-overhaul/ERL_550/OTP-14019:
  Update types for posix error codes

I have read the man pages for most socket and file operations
on recent Linux, FreeBSD, OpenBSD and Solaris 10 and noted
the possible error codes.

Which error codes that are possible for file operations have
been updated in file:posix/0.  Error codes for socket operations
in inet:posix/0.  The latter refers to the former so it is
a superset, assuming that e.g sendfile and AF_UNIX socket
operations could cause socket operations to return any file
error code.  That is not entirely true, but could be,
especially in the future.

Added to file:posix/0 are:
  ebadmsg edeadlk edeadlock eftype emultihop enobufs enolck enolink
  enosr enostr enosys eopnotsupp eoverflow erange etxtbsy

Added to inet:posix/0 are all but:
  exbadport exbadseq file:posix()

These are still possible according to erl_posix_str.c,
but are not in file:posix/0 nor in inet:posix/0,
and many of them are not file nor inet related, but some might be:
  e2big eadv ealign ebade ebadfd ebadr ebadrpc ebadrqc
  ebadslt ebfont echild echrng ecomm edirty
  edom edotdot eduppkg eidrm einit eisnam
  elbin el2hlt el2nsync el3hlt el3rst
  elibacc elibbad elibexec elibmax elibscn elnrng
  enavail enet enoano enocsi enodata enoexec
  enonet enosym enotempty enotnam enotuniq
  eproclim eprocunavail eprogmismatch eprogunavail
  erefused eremchg eremdev eremote eremoteio
  eremoterelease erpcmismatch erremote eshutdown
  esrmnt esuccesss etime etoomanyrefs
  euclean eunatch eusers eversion exfull
  sysnotready vernotsupported ediscon enomore
  ecancelled einvalidproctable einvalidprovider eproviderfailedinit
  syscallfailure service_not_found type_not_found e_no_more
  e_cancelled unknown

[ERL-557] add is_empty/1 to sets and ordsets
OTP-14996, ERL-557, PR-1703

It has been decided that it was to early to deprecate the old
string functions.

This partially reverts commit ccb3f7f9768d3c28783c771df47eec1829e51802.

* maint:
  Updated OTP version
  Update release notes
  Update version numbers
  ssh: Fix bad spec for double_algs() in ssh.hrl
  Test event insert from init
  Fix init to allow all actions

Conflicts:
	OTP_VERSION

stdlib: Add function lists:search/2