Proto: expand constants before typecheck and normalization

Context

@arvidnl discovered a bug (described in #1709 (closed)) where typechecking and normalization don't work with global constants. This MR fixes the issue.

Manually testing the MR

Repeat the steps in #1709 (closed) - they will work. Specifically: Create a file ./contract.tz with the following contents:

parameter (constant "exprvKFFbc7SnPjkPZgyhaHewQhmrouNjNae3DpsQ8KuADn9i2WuJ8");
storage (constant "exprvKFFbc7SnPjkPZgyhaHewQhmrouNjNae3DpsQ8KuADn9i2WuJ8");
code {
       DROP;
       PUSH unit (constant "expruJpGVgueH6vjZDZQRjgXUuHBi4Y6UQ3cbz6swP2FMVybvnDjm5");
       NIL operation;
       PAIR;
     }

Then the following shell code:

# setup
create_mockup () {
                      	if [[ ! -d /tmp/mockup ]]; then
                      		tezos-client \
                      		  --protocol ProtoALphaALphaALphaALphaALphaALphaALphaALphaDdp3zK \
                      		  --base-dir /tmp/mockup \
                      		  --mode mockup \
                      		  create mockup
                      	fi
                    }
alias client = "create_mockup && tezos-client --mode mockup --base-dir /tmp/mockup"
client register global constant unit from bootstrap1 --burn-cap 3
client register global constant Unit from bootstrap1 --burn-cap 3
# test
client typecheck script ./contract.tz
client normalize script ./contract.tz

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
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