feat: shadowing gno1

[petar-dambovaliev]

After a discussion with @jaekwon, we reached a conclusion that for gno, we want to allow shadowing of identifiers which are defined in a local scope. This means that a user cannot shadow any global identifiers and therefore uverse identifiers.
The main reason for this is one of readibility and security, as people tend to think they know what something is and not verify.
Allowing local scope shadowing will be sufficient for minimizing the ergonomics impact.

Relevant issues
#1758
#1091

The side-effects of this decision means that whenever we add a new uverse identifier, it would be a breaking change.
As far as gno2, which is not yet clearly defined, we plan to have a rule as capitalized identifiers to be excluded from shadowing.

[jaekwon]

Thank you Petar1!
There is still the issue of whether to allow or disallow package level global shadowing.
uverse global > package level global > func decl locals >= other block locals.
We might deviate from Go and not support new globals after launch.
Maybe they can still be supported with directives.

[petar-dambovaliev]

The first iteration was done. This issue can stay open for the rules mentioned above that are for gno2