Refactor: Remove Rc from PreAccount and InvokeContext::get_account()

[Lichtso]

Problem

Rc<RefCell<AccountSharedData>> in the program-runtime is overkill and AccountSharedData would suffice for the PreAccounts. Also InvokeContext::get_account() does not need to clone the Rc.

This PR is a spinoff / preparation for #21706.

Summary of Changes

• Moves the .clone() of the AccountSharedData from PreAccount into InvokeContext.
• Replaces Rc<RefCell<AccountSharedData>> by AccountSharedData in the PreAccounts.
• Splits get_account() into find_index_of_account() and get_account_at_index() in order to remove Rc from return type.

Fixes #

[codecov]

Codecov Report

Merging #21882 (ab3476b) into master (033106e) will decrease coverage by 0.0%.
The diff coverage is 54.2%.

@@            Coverage Diff            @@
##           master   #21882     +/-   ##
=========================================
- Coverage    81.3%    81.3%   -0.1%     
=========================================
  Files         516      516             
  Lines      144217   144216      -1     
=========================================
- Hits       117268   117257     -11     
- Misses      26949    26959     +10