Naming-aware term pretty-printing.

[brianhuffman]

Add some new functions for pretty-printing shared terms using information from the SAWNamingEnv to choose best aliases for names.

This PR avoids changing the types or behavior of any existing functions, in order to avoid requiring PRs for five other packages.

[brianhuffman]

So far, this lets us avoid some of the redundant qualified names in saw-core pretty printing (#17). This is limited by the fact that only defined saw-core constants are registered in the SAWNamingEnv at the moment, and we are not yet registering axioms, primitives, datatypes, or data constructors.

sawscript> print_term {{ sum [1..10] + 0x23 }}
[23:47:41.877] let { x@1 = Prelude.Vec 8 Prelude.Bool
      x@2 = Cryptol.TCNum 1
      x@3 = Cryptol.TCNum 8
      x@4 = PLiteralSeqBool x@3
      x@5 = PRingSeqBool x@3
      x@6 = Cryptol.TCNum 10
      x@7 = tcAdd x@2 (tcSub x@6 x@2)
    }
 in ecPlus x@1 x@5
      (sum x@6 x@1 (PEqSeqBool x@3) x@5
         (Prelude.coerce (seq x@7 x@1) (Prelude.Vec 10 x@1)
            (seq_cong1 x@7 x@6 x@1
               (Prelude.unsafeAssert Cryptol.Num x@7 x@6))
            (ecFromTo x@2 x@6 x@1 x@4 x@4)))
      (ecNumber (Cryptol.TCNum 35) x@1 x@4)