[evm] attributes related to EVM should have indicative names about move

[wrwg]

My thinking is to make attributes general context-sensitive. So we would have something like

#[evm_contract] // indicates that attributes in this module are related to EVM
module M {
  #[callable] // interpreted in the context of evm_contract
  public fun f(...) { ... }
}

Thoughts?

[vgao1996]

@wrwg sorry for the late reply. I think you made a good point that attributes are just strings interpreted by individual tools, so there isn't really that much of an inherent namespace pollution issue here.

Using less verbose (and therefore more general) attribute names will likely make the program look cleaner to people who are familiar, but may confuse newcomers or cause trouble if we want to introduce a similar set of attributes for a different target platform/language and have them present in the same module, but for now I don't think this is a real problem and I like the conciseness of the context-sensitive approach so let's just move forward with it. We can make adjustments should needs arise.