RFC: Improving hints related to $parse

[btford]

Problem

Parsers are hard.

Current solution

Decorate $parse and use regexes to do naive checks on expressions.

Ideal solution

Regexes aren't powerful enough. Instead, we should replace the implementation of $parse with our own implementation that both logs helpful information and also does proper parsing. This is challenging because we'd possibly have to support a debug version of $parse for each version of Angular to ensure that we preserve existing behavior.

[SomeKittens]

Another thing to note is that we don't want to be throwing these hints every digest cycle.