New JSONPointer tests needed

[stleary]

After #1078 is merged, add these unit tests to document the change:

input	before 1078	after 1078
/~01, #/~01	selects key /	selects key ~1
/~00, #/~00	selects key ~	selects key ~0
/a~01b	selects a/b	selects a~1b
/a~00b	selects a~b	selects a~0b
builder().append("~1")	selects /	selects ~1
builder().append("~0")	selects ~	selects ~0
new JSONPointer(List.of("~1"))	selects /	selects ~1