JSON is a data format, I don't think it's supposed to have comments ever. A simple parser drops newlines, and finds your comment that is not a valid JS object so it complains. It's possible the parser may recognize C style comments /* Like This */, but there's no reason for comments in JSON, especially INSIDE an array.
They are not spawning with full inventory. In my earlier test I threw a carrot at the newly spawned villager, and he picked it up instantly and planted it.
I do not think this is related to 20190. I have spawned brown robe villagers in creative, thrown seeds at them which they will not pick up. I also planted wheat, watched the villager harvest and leave seeds behind.
I found one additional thing with this. I was taking screenshots as I noticed my items did show in my hands, different than the original post.
Just before I went to open the chest, I dropped the boots, picked them up, opened the chest, and attempted to put them into the chest (which crashed the game)
After reloading, I saw the boots on the ground where they had been thrown earlier, and I had a duplicate in my hands.
I tried reproducing the duplication, but it did not work. I dropped the duplicate, and will try again after it despawns.
I've had this same thing happen on Android. I have never used the Classic UI. I first noticed the bug when I tried to enchant some diamond armor, I had made a diamond helmet and shoes earlier, removed them, and they did not show on the enchantment table screen. I came to realize that although I could see them on the inventory screen, I was not able to place them in chests either. Moving them to the hotbar will show the item in your hand, but the hotbar slot appears to be empty.
If you open a chest, the item will not be visible. If you determine which slot it is in, you can tap it in the chest dialog and it will show the name, however if you then try to hold that slot to transfer to the chest it will crash. The only thing you can do is wear the armor, or drop it on the ground. It never takes damage. I belive I also tried throwing it into a hopper which also crashed the game.
I had earlier gotten rid of an unenchanted helmet with this bug by dropping it and letting it despawn. Now I have an enchanted pair of boots in my inventory with the same bug.
I have no idea how to duplicate this bug currently.
In my world I found cats in two towns that were being generated post-update, however I recently visited at least seven "older" towns looking for cats, and found none. I have at least three of those towns are in base areas where I spend a large amount of time, so I would expect to see an excess of them just as we see new foals on Horse Island and new calves on Sheep Island all the time.