Drop in replacement of eval.php based on psysh

Drop in replacement of eval.php based on psysh

eval.php is meant to eval() commands in MediaWiki global scope. We had
at least a couple attempts to move it to a regular Maintenance script.

As noted on the revert commit b475e930 r54839, using a Maintenance
script drop us in the callee function scope instead of the global scope
which is a hard requirement.

http://psysh.org/ is a Read-Eval-Print-Loop with color highlight, modern
code and more.

Add maintenance/shell.php script as MediaWikiShell class.

Passing command from stdin is supported.
Execution is forked for graceful handling of PHP fatal errors.
Colors!!
Support the undocumented '-d' arguments from eval.php:
  0 set $wgDebugLogFile to stdout. Eval.php used /dev/stdout, make it
    php://stdout in the new script.
  1 additionally set DBO_DEBUG on all the database load balancer servers

PHP globals have to be whitelisted which is not supported out of the box
by Psy. Upon request, the author of PsySh, Justin Hileman, kindly
provided a pass to inject globals (with the exceptions of super
globals). He agreed for code reuse:
    https://github.com/bobthecow/psysh/issues/353
The code was added to maintenance/CodeCleanerGlobalsPass.inc

Note that this is not a perfect simulation of global scope (but pretty
close): variables declared in the shell which did not exist before
won't be global unless the 'global' keword is used.

Example usage:

$ php maintenance/shell.php

>>> $wgFullyInitialised
=> true

>>> $hashar = User::newFromName( 'hashar' )
=> User {#274
     +mId: null,
     +mName: "Hashar",
     ...

>>> ls --long --all $h
<descriptive output of all object properties/methods>

Bug: T117661
Signed-off-by: Justin Hileman <justin@justinhileman.info>
Signed-off-by: Gergő Tisza <tgr.huwiki@gmail.com>
Change-Id: I3d6d42e138d3cc4a0aaafdd7f5f97cb17d8b8cb3