fix: Fix Composite on IE11

[diegohaz]

This PR fixes several issues with Composite and its derivative components on IE11, mostly related to the way events were created and fired. IE11 doesn't support event constructors.

This also makes sure that intermediate focus/blur events will be ignored for consistency between roving tabindex and aria-activedescendant approaches.

Does this PR introduce a breaking change?

No

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[codecov]

Codecov Report

Merging #609 into master will decrease coverage by 0.54%.
The diff coverage is 82.22%.

@@            Coverage Diff             @@
##           master     #609      +/-   ##
==========================================
- Coverage   95.64%   95.10%   -0.55%     
==========================================
  Files         122      123       +1     
  Lines        2089     2144      +55     
  Branches      622      633      +11     
==========================================
+ Hits         1998     2039      +41     
- Misses         91      105      +14     

Impacted Files	Coverage Δ
packages/reakit/src/Tabbable/Tabbable.ts	88.33% <ø> (ø)
...rc/Composite/__utils/getNextActiveElementOnBlur.ts	66.66% <66.66%> (ø)
packages/reakit/src/Menu/MenuItem.tsx	82.97% <70.00%> (-1.81%)	⬇️
packages/reakit/src/Composite/Composite.ts	89.16% <78.84%> (-8.34%)	⬇️
packages/reakit/src/Composite/CompositeItem.ts	90.43% <100.00%> (+0.71%)	⬆️
...eakit/src/Composite/__utils/findEnabledItemById.ts	100.00% <100.00%> (ø)
packages/reakit/src/Radio/Radio.ts	100.00% <100.00%> (ø)

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