handle events without deprecated keyCode property

[nightwing]

fixes #4952

I have verified that list of keys have not changed as a result of this pull request, by running the following in browser console and comparing output with the version before this pull request

          q = require("ace/lib/keys");
          delete q.default;
          delete q.$codeToKeyCode;
          var sortByKeys = function(obj) {
                if (!obj || typeof obj != "object" || Array.isArray(obj)) {
                    return obj;
                }
                var sorted = {};
                Object.keys(obj).sort().forEach(function(key) {
                    sorted[key] = sortByKeys(obj[key]);
                });
                // assert(_.isEqual(obj, sorted));
                return sorted;
            };
             JSON.stringify(sortByKeys(q))

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.66%. Comparing base (6a26b27) to head (0a610db).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5543   +/-   ##
=======================================
  Coverage   86.65%   86.66%           
=======================================
  Files         593      593           
  Lines       42873    42898   +25     
  Branches     7123     7125    +2     
=======================================
+ Hits        37151    37176   +25     
  Misses       5722     5722           

Flag	Coverage Δ
unittests	86.66% <100.00%> (+<0.01%)	⬆️

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