Rename and move cx export/trampoline files

[nroggeman-ledger]

Description

The goal of this PR is to change some file names in Cx library exported, and to move some other files in the OS, because they don't belong to the SDK (OS part of the trampoline mechanism)

Changes include

• Bugfix (non-breaking change that solves an issue)
• [*] New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.88%. Comparing base (df1488d) to head (36bbf8c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #756   +/-   ##
=======================================
  Coverage   59.88%   59.88%           
=======================================
  Files          12       12           
  Lines        1710     1710           
=======================================
  Hits         1024     1024           
  Misses        686      686           

Flag	Coverage Δ
unittests	59.88% <ø> (ø)

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