InputDecorator M3 tests migration - prefixIcon/suffixIcon (#149437)

## Description

This PR adds several tests tp check M3 specification compliance for `InputDecorator.prefixIcon` and `InputDecorator.suffixIcon`.

This is somewhat repetitive but it helped me to catch several styling and positionning issues, I added TODOs because I will file the fixes once this PR is merged (just in case the fixes break some Google tests). 

## Related Issue

Part of flutter/flutter#139076