Ok I'll give this one more shot.
Here are the answers to your questions directly as there is a lot of speculation on this forum lately
Does anyone on this forum have experience lifting using these attachment points?
Yes many here have done this and have experience doing it just search the archives.
Are these attachment points strong enough to support the boat while I pull the trailer out from underneath?
Yes they are strong enough provided you have not modified anything and your bow eye is not rotten.
Your bow eye is reinforced in the hull with a wooden block that fits right in the V of the bow. Depending on age this may rot and if so needs replacing regardless. If you have an older boat and the bow reinforcement is not already done to link the forestay chainplate to the bow eye now is the time to make this repair.
The stern gudgeon is reinforced on the inside. your stern is made of about 1/4 inch glass, then 1/2 plywood, glassed in. there is then a brass plate glassed into there which the 4 bolts thread into. If removing a gudgeon use threaded rod or the plate will fall causing you to have to cut through the transom to reinstall as often the glass that held it in place has given way. If lifting the boat by these points I would recommend re-bedding these fittings once done.
Floating the boat is the easiest way but if you are wanting to do this all on land there are many ways to do this. Remove the keel, lift with blocks, use stands, use engine hoists, trees, etc... I believe the tech manual has at least 3 different way that this can be accomplished and Youtube has a number of examples as well. If your going to remove the boat on land save yourself the headache of doing it again a few years and drop your keel, replace the hanging hardware and the cable, inspect your turning ball etc... All of these are regular maintenance items and more easily done with the boat off the trailer.
These boats are only reinforced in a few areas so bunk placement and length is crucial to prevent the oil canning. Again this is referenced in the archives here as well as in the Tech Manual. Having good bunks is crucial to having a successful trailer sailer. The beauty of this boat is that you can hitch it up and just go if your rig is in order and you keep your boat deciently maintained. Many trailer thousands of miles each year with these boats and have no issues with oil canning. If you want local help reach out to Fleet 4 there in Sacramento. They will have a wealth of information and likely even the hands to help you fix whatever you need. C22 sailors are like a family.
I hope this all helps and I would recommend also asking your question on the FB group as most from this forum have migrated that way for a number of reasons.