ieee_floatt: add preconditions

[kroening]

This adds preconditons to further binary operators in ieee_floatt that the format must match.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.55%. Comparing base (d5cf498) to head (08a010d).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8540      +/-   ##
===========================================
- Coverage    78.58%   78.55%   -0.03%     
===========================================
  Files         1729     1729              
  Lines       199635   199714      +79     
  Branches     18311    18312       +1     
===========================================
+ Hits        156887   156892       +5     
- Misses       42748    42822      +74     

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