InputDecorator M3 tests migration - Step5 - Helper/Counter/Error (flutter#144932)

## Description

This PR migrates `InputDecorator` helper/counter/error related tests to M3 and adds some missing tests.

It is the fifth step for the M3 test migration for `InputDecorator`.
Step 1: flutter#142981
Step 2: flutter#143369
Step 3: flutter#143520
Step 4: flutter#144169

## Related Issue

Related to flutter#139076
fixes flutter#138213

Author: bleroux