Move blink::serializedCharacterData array to read-only data segment
This array is logically const but was not marked as such. Marking it as
const lets the compiler/linker store it in the read-only data segment,
which is strictly better than being in read/write memory. This change
moves 11,844 bytes from the .data to .rdata segment.
Note that "const" implies static which is why "extern const" is needed.