fix(ripple): Fix nested ripple handling to work with touch events

[kfranqueiro]

This reorders code so that the logic that prevents redundant ripple activation from simulated mouse events after a delay on touch devices can function in tandem with the logic which prevents simultaneous activation of nested parent/child ripples.

To see what this fixes, go to list.html, scroll down to the checkbox example, and tap on one of the checkboxes using touch input. The list item should not also ripple at the same time.

I also found and cleaned up a couple of confusing variable declarations (and one excess variable due to one of them).

[codecov-io]

Codecov Report

Merging #2178 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #2178   +/-   ##
=======================================
  Coverage   99.14%   99.14%           
=======================================
  Files          90       90           
  Lines        3843     3843           
  Branches      497      497           
=======================================
  Hits         3810     3810           
  Misses         33       33

Impacted Files	Coverage Δ
packages/mdc-ripple/foundation.js	100% <100%> (ø)	⬆️

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[patrickrodee]

LGTM!