uninitialized-local reports false positives for structs

[snd]

given StructType a common pattern is:

StructType memory structVar;
structVar.a = 1;
structVar.b = "a";

slither reports uninitialized-local for StructType memory structVar in this case.

a useful addition would be to check for each struct field whether it is assigned below before it is read.

alternatively this detector could detect that locals (and storage variables) are initialized before they are read instead of checking that they are initialized in the line they are defined.
this should result in catching all dangerous unintended reads from uninitialized variables while producing less noise.
when handling structs it could treat each field separately.

the same could be done for uninitialized-state.

[montyly]

Duplicate of #365