Transpile destructuring patterns in param lists that have default values.

Note, this is not about default values IN the pattern, e.g.

function f([a, b=1, c]) {}

which already worked, but about default values for the entire pattern, e.g.

function f([a, b, c] = [0, 1, 2]) {}
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=75303254