8013914: Removed explicit LineNumberNodes that were too brittle when code moves around, and also introduced unnecessary footprint. Introduced the Statement node and fixed dead code elimination issues that were discovered by the absense of labels for LineNumberNodes. Reviewed-by: jlaskey, attila

x = undefined
y = undefined
z = undefined
s = undefined
u = undefined
r = undefined
t = undefined
ReferenceError: "q" is not defined
b = 10
ReferenceError: "b" is not defined
Value of 'a' inside the function 20
Value of 'a' outside the function 10