Why Shakespeare used "come" in the line "A Daniel come to judgement?"
Solution 1:
A Daniel come to judgment!
Note first that this is not a sentence, a finite clause, but an exclamatory noun phrase, just like the immediately following Yea, a Daniel!. Come to judgment isn't a predicate but an adjectival modifying Daniel.
Your "perfect tense with the auxiliary verb omitted" is a pretty good guess: lots of linguists treat come to judgment here as a relative clause 'reduced' by 'Whiz-deletion':
A Daniel
who iscome to judgment.
(Note that in Early Modern English the perfect of many intransitive verbs of motion, like come, was constructed with BE as the auxiliary: the Lord is come.)
I myself do not concur in this parsing: I understand come as a past participle deployed as an adjective. Since the verb is intransitive it bears an active rather than a passive sense. ... But it doesn't really matter at this level of analysis which parsing you employ: the sense is the same.
And, yes, it was a common syntactic phenomenon in Shakespeare's day. It is still encountered occasionally, though I think a bit more often in British English than US English:
Here's a man come about the job you advertised.
Solution 2:
As a British English speaker I would consider "come to", that is " has arrived at this place" to be an archaic form and not common usage, except perhaps in legal speak - renowned for its resistance to change!
So:
A Daniel come to judgment!
This [I think - I don't know the play in detail] is said by Shylock sneeringly and suggests that Daniel has been found-out or judged [possibly in a court of law but probably by the other 'young' character - Shylock is congratulating them on their good judgment - possibly ironically]:
O wise young judge, how I do honour thee!
I detect some Shakespearian irony at play, Shylock referring to the other character as a "wise young judge", possibly implying in reality, someone that is inexperienced, but that has made a [obvious?] wise decision or come to a good conclusion about the situation [Daniel's motives].
yea, a Daniel!
Is an abbreviated form of "Yea verily", again an archaic form used widely in Shakespeare's time as:
"An Exclamation used to either [affirm] the [preceding] statement. or to [imply] the statement to be made immediately after has greater significance to the audience in question.