Cosmetic compiler cleanup

[Clyybber]

Summary

• SomePNodeOrPType.sons[...] ->. SomePNodeOrPType[...]

• SomeIndexable[SomeIndexable.len - x] -> SomeIndexable[^x]

• Removed L/length variables where they went unused due to the above change

• Removed the PTransfNode type from transf.nim

• Removed addSon and replaced it with add since it is the same

• Changed all add calls to use method call syntax

• Changed all len/safeLen calls to use method call syntax

• Changed ranges of the form x..something.len-(y+1) to x..<something.len-y

[narimiran]

Regarding the "Unify range operators" commit — I would like to see it unified in the opposite direction, with spaces before and after .. and ..<, as that is the recommended style.

[Clyybber]

@narimiran I think x..y/x..<y captures the idea of a range better, since the operator is connecting both ends, as opposed to x .. y/x ..< y.