Generalize assert syntax in analyzer

[eernstg]

With reference to #17682 for background, the analyzer should be adjusted such that it accepts arguments to assert parsed as expression, rather than requiring the more restrictive conditionalExpression.

The language team discussed this issue and came up with an analysis concluding that we will make this change: https://gist.github.com/eernstg/50a327addd96035d5393a507c0ea2d9a.

[bwilkerson]

https://codereview.chromium.org/2140673004/