`get` keyword behaves exactly like `method_id` (auto-calc hash),
but it's placed on the left, similar to Tact: `get T name()`.
`method_id(n)` is still valid, considering it can't be invoked by name,
since a client will compute another hash.
It's supposed it will be still used in tests and in low-level code
(not to be called externally, but to be called after replacing c3).
`get(hash)` is invalid, this keyword does not accept anything.
This will allow to easily implement camelCase wrappers aside stdlib,
even without changing hashes of existing contracts.
Also, stdlib renamings could be easily performed in the same manner,
even with arguments reordered.
