Redesign displayValue/warnings

[patrickhulce]

@brendankenny expressed some concerns over our displayValue/warnings display methods over in #5132 (review)

two things

1. visually associating of displayValue + audit title

A few major things for how we handle these different outputs:

It's great to start using displayValue for things that are display values, but it does expose a weakness with how we display them. It's definitely harder to scan across to the value for the audit vs just having it right below

old:

new:

(and it's even wider across when not shrunk by github)

2. warnings at the top of the report

Separating the warnings from the audits seems like a regression from the status quo in most of the warnings cases added here. Having a list of images we can't reencode at the top of the report or (in the case of sample_v2.json) a warning that some target=_blank anchors may be outgoing but we can't tell, seems like noise at the top of the report and is lost as valuable context at the individual audit level (where you probably want to be warned that the audit may have been unable to comprehensively run its test).