InputDecorator M3 tests migration - Step3 (#143520)

## Description

This PR is the third step for the M3 test migration for `InputDecorator`.
Step 1: https://github.com/flutter/flutter/pull/142981
Step 2: https://github.com/flutter/flutter/pull/143369

This PR moves some tests out of the 'Material2' group (the ones that are ok on M3).
@justinmc The diff is almost unreadable, I moved the tests as carefully as possible and I checked that before and after the number of tests is exactly the same. 

## Related Issue

Related to https://github.com/flutter/flutter/issues/139076

## Tests

Move some tests from 'Material2' group to main().