Use reader-monad bracketing combinators for extending bound variable environment in translator

[brianhuffman]

Currently the term translation monad is just a state monad, and the local variable environment is just one of the fields in the mutable monad state, which can be updated at any time. As @eddywestbrook suggests in the comment thread of GaloisInc/saw-core-coq#29, it would be more principled to use reader-monad-style operations to manage the local variable environment. Following this discipline will make the code easier to understand and make errors easier to avoid.

So instead of

translateAndBindName :: String -> m Ident

we should use only bracketing combinators like

withTranslatedName :: String -> (Ident -> m a) -> m a

that explicitly delimit the scope of the Ident that is added to the local environment.

[eddywestbrook]

Closed by #1928