JS: fix bounds checking (Issue 23123)

* For ByteArray-based bounds-checking, the JavaScript backend must use the
`len` field, instead of the inbuild JavaScript `length` field.

* Range-based operations must also check both the start and end of the range
for bounds

* All indicies are valid for ranges of size zero, since they are essentially no-ops

* For cases of ByteArray accesses (e.g. read as Int), the end index is
(i * sizeof(type) + sizeof(type) - 1), while the previous implementation
uses (i + sizeof(type) - 1). In the Int32 example, this is (i * 4 + 3)

* IndexByteArrayOp_Word8As* primitives use byte array indicies (unlike
the previous point), but now check both start and end indicies

* Byte array copies now check if the arrays are the same by identity and
then if the ranges overlap.