This already worked fine. Now it's tested.
I did have to teach `jbig2` to correctly generate test files for this.
See the PR adding these tests for local changes.
I used the script from #23659 to create these images, but I replaced
these lines:
```
-txt -Param -numInst 4
-ID 2 108 50 -ID 3 265 60 -ID 1 100 135 -ID 0 70 232
-txt -Param -RefCorner 2
```
For `bottomleft`, I replaced them with:
```
-txt -Param -numInst 4
-ID 2 137 50 -ID 3 294 60 -ID 1 199 135 -ID 0 319 232
-txt -Param -RefCorner 0
```
For `bottomright`, I replaced them with:
```
-txt -Param -numInst 4
-ID 2 108 50 -ID 3 265 60 -ID 1 100 135 -ID 0 70 232
-txt -Param -RefCorner 2
```
For `topright`, I replaced them with:
```
-txt -Param -numInst 4
-ID 2 108 79 -ID 3 265 89 -ID 1 100 234 -ID 0 70 351
-txt -Param -RefCorner 3
```
All three new files display fine in Chrome.
The bottomleft one displays fine in Firefox, while the other two
look compressed in X. I think this is a bug in pdf.js that I'll
report upstream.
(Reportedly they look fine in Acrobat on Android.)
67875ecb6f