Refactor: InstructionAccount indices

[Lichtso]

Problem

The property index of InstructionAccount should be called index_in_transaction.
Also, we currently search for the index_in_caller in the program runtime multiple times and could be reusing them.
Thus it makes sense to introduce an index_in_caller property as well.

Summary of Changes

• Splits index of InstructionAccount into index_in_transaction and index_in_caller.
• Adds more helpers and convenience methods to transaction_context.rs

Fixes #

[codecov]

Codecov Report

Merging #22165 (aef014d) into master (29edb13) will decrease coverage by 0.0%.
The diff coverage is 33.5%.

@@            Coverage Diff            @@
##           master   #22165     +/-   ##
=========================================
- Coverage    81.1%    81.0%   -0.1%     
=========================================
  Files         523      523             
  Lines      146370   146459     +89     
=========================================
+ Hits       118747   118762     +15     
- Misses      27623    27697     +74