Optimize access of struct fields in storage

[cburgdorf]

What is wrong?

When accessing struct fields in storage we are currently calculating storage pointers in YUL (which the optimizer doesn't optimize away)

fe/compiler/src/yul/mappers/expressions.rs

Line 472 in fa7c3c1

expression! { (add([ptr], [offset])) }

How can it be fixed

1. We could pre-calculate them
2. Alternatively we might end up optimizing this another way as soon as we start storing structs tightly packed

[Y-Nak]

will be resolved in #676
Both 1. and 2. will be realized.