A sloppy-mode function called with undefined or null as this reads the
global object. Element reads of that this, or of a variable it initializes,
now reach the program's lookup too: a literal key (`this["Map"]`) adds that
name, and a computed key (`this[name]`) installs the lookup for every
declared global, as `globalThis[name]` does. Before, a literal key read the
opaque identity token and a computed key threw SC2020.
Chris Tate
0f47b9cbab