This patch includes:
* Making it possible to access offsets of a DNONE (returning a DNONE)
* Initializing user-defined variables as DNONE inside short-circuited branches
* Make DNONE propagate with other operators
* Make DNONE count as false for logic operators
* Remove a now-outaded bit in doLevelAtom. In case of shortcircuit,
$result is now DNONE instead of DNULL, and thus it's possible to
access offsets of it. Performance++!
* Don't allow modifying or adding an element of a DNONE as if it were an
array (to avoid inconsistencies)
This re-applies Id85c673337fa90a3782fd22eb9690cd996967111 with several fixes.
NOTE: Haven't tested locally, although I'm pretty confident thanks to
the amount of tests added.
Bug: T214674
Bug: T228677
Change-Id: I5ec4ab44c4e88aaf18c0d7b73355d27050beeda7
