Strong mode should infer parameter types from default value expressions

[stereotype441]

Currently, strong mode does not infer the type of the parameter x in the code below:

void f({x: false}) {
  ...
}

It seems like it would be reasonable to do so, since it would be similar to the way it infers the type of variables from their initializer expressions.

[jmesserly]

Nice, yeah, we probably just forgot about this AST node.

[jmesserly]

Doh, I just hit this while implementing/testing #25573 (no-implicit-dynamic). I may roll in a fix or look at it concurrently.

[jmesserly]

update, fixed it in resolver & element summaries, still haven't got it working in AST-based summaries yet.

[jmesserly]

https://codereview.chromium.org/2092333002/ -- but I might be way off on that approach :)