The list of normal contractions is relatively small (sorry the forum doesn't like tables but you can find it
here):
aren't are not
can't cannot
couldn't could not
didn't did not
doesn't does not
don't do not
hadn't had not
hasn't has not
haven't have not
he'd he had; he would
he'll he will; he shall
he's he is; he has
I'd I had; I would
I'll I will; I shall
I'm I am
I've I have
isn't is not
let's let us
mightn't might not
mustn't must not
shan't shall not
she'd she had; she would
she'll she will; she shall
she's she is; she has
shouldn't should not
that's that is; that has
there's there is; there has
they'd they had; they would
they'll they will; they shall
they're they are
they've they have
we'd we had; we would
we're we are
we've we have
weren't were not
what'll what will; what shall
what're what are
what's what is; what has
what've what have
where's where is; where has
who'd who had; who would
who'll who will; who shall
who're who are
who's who is; who has
who've who have
won't will not
wouldn't would not
you'd you had; you would
you'll you will; you shall
you're you are
you've you have
There are multiple duplications that allow a handful of regex's to cover the list. I actually had a saved search group that did this - it was only a half-dozen or so steps. Unfortunately, I lost the group when my hard drive was replaced and haven't recreated it yet.