Add DMUL and DDIV overload

[lupino3]

As a first step, simplify instruction building by using a dictionary rather than a giant switch statement.

Will fix #867.

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (9c934ab) 52.00% compared to head (90f9b6a) 51.85%.
Report is 12 commits behind head on master.

❗ Current head 90f9b6a differs from pull request most recent head 1bd934c. Consider uploading reports for the commit 1bd934c to get more accurate results

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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #871      +/-   ##
============================================
- Coverage     52.00%   51.85%   -0.16%     
+ Complexity     1451     1386      -65     
============================================
  Files           251      251              
  Lines         10237    10134     -103     
  Branches       1101     1101              
============================================
- Hits           5324     5255      -69     
+ Misses         4590     4556      -34     
  Partials        323      323              

Files	Coverage Δ
...java/org/edumips64/core/is/InstructionBuilder.java	98.34% <98.13%> (+14.41%)	⬆️

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