SIMD-0321: Provide pointer to instruction data in VM r2

[buffalojoec]

Implementation of SIMD-0321, which provides a pointer to the instruction data in the VM's register 2.

[mergify]

The Firedancer team maintains a line-for-line reimplementation of the
native programs, and until native programs are moved to BPF, those
implementations must exactly match their Agave counterparts.
If this PR represents a change to a native program implementation (not
tests), please include a reviewer from the Firedancer team. And please
keep refactors to a minimum.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.25000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.9%. Comparing base (3684e58) to head (2249bcf).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #7009     +/-   ##
=========================================
- Coverage    82.9%    82.9%   -0.1%     
=========================================
  Files         823      823             
  Lines      360873   360908     +35     
=========================================
+ Hits       299369   299381     +12     
- Misses      61504    61527     +23     

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[LucasSte]

Suggested change

	let instruction_data_len = *((instruction_data_addr as u64 - 8) as *const u64);
	let instruction_data_len = *(instruction_data_addr.sub(8) as *const u64);

[buffalojoec]

Can you guys give full reviews please, instead of these fly-by one-off comments? I'd rather just resolve everything once.

[buffalojoec]

Also, this is pedantic.

[LucasSte]

I reviewed your entire PR. That was the only comment that I had.