Fix AARCH64 Keystone Vector Instructions bug

[rbs-alexr]

• [X] I have reviewed the OFRAK contributor guide and attest that this pull request is in accordance with it.

One sentence summary of this PR (This should go in the CHANGELOG!) When capstone disassembles the bytes for the following instruction "movi v0.2d #0" it represents it as "movi v0.0x2d #0" which causes keystone to throw an "Unknown Operand" error.

Link to Related Issue(s) N/A

Please describe the changes in your request. I added some processing to the assembler_service_keystone to work around this capstone bug

Anyone you think should look at this, specifically? @whyitfor

[rbs-alexr]

To provide some context to the most recent commits. The erroneous behavior we were observing was not due to keystone, it was due to our own _asm_fixups function in disassembler_service_capstone. We had regex to convert constants to their hex values, which breaks for vector instructions. The new code skips this conversion if the mnemonic is from a list of known AARCH64 vector instructions