SME SVCR logic fix

[FinnWilkinson]

This PR for the most part addresses issue #329 - correcting the SVCR and Streaming Mode logic introduced with SME. This is summaried as:

• If a program is in Streaming Mode and calls SMSTART again, ZA and Vector registers are not zeroed out.
• SVE Vector registers (and their aliases such as NEON and Scalar registers) are only zeroed out when SVCR.SM bit changes
• SME's ZA register is only zeroed out when SVCR.ZA bit changes
• SVCR can now be correctly updated using a regulat msr svcr, xt instruction in addition to smstart/smstop/msr svcr, #imm
• More tests surrounding the SVCR logic have been added

Additional to this, logic for the NEON muti-struct store with post index instructions introduced in PR #335 has been corrected via a small change to the metadata to correctly identify if a #imm or xt is used as said post index.

NOTE: this branch is based on macos-sst-build-fix and thus contains the fixes present in PR #338. This PR will be rebased to dev once PR #338 has been merged and should be merged into dev after PR #338.

[JosephMoore25]

Looks mostly good, but tiny code inconsistency.

You define "const Architecture& arch = instruction_.getArchitecture();" but then still use instruction_.getArchitecture() a couple lines later and then switch to arch a bit later. Probs best to just stick to one or the other for the sake of consistency.

[ABenC377]

Can 'instruction_.getArchitecture()' in ExceptionHandler.cc line 661 be replaced with the 'arch' variable declared above it?

[FinnWilkinson]

@JosephMoore25 @ABenC377 Good spot, will change this now

[dANW34V3R]

One comment