Resolves folder options (i.e. --modules-folder) relative to cwd (#7074)

[mbpreble]

• Prevents potentially surprising behavior and data loss

• Includes integration test verifying that user-reported data loss scenario does not occur

Summary
Motivated by high severity issue #7074, following recommended approach by @arcanis of resolving all folder options relative to the cwd (instead of potentially relative to the nearest project root). Adds an integration test illustrating there are no yarn failures, data loss, or other surprising behaviors in the scenario reported in the issue.

Test plan

It's relatively straightforward to reproduce the reported issue with a current version of yarn:

#! /bin/sh

# Create a project with a lib folder
mkdir -p my-project/my-lib

# My project is some sort of project
echo "{}" > my-project/package.json
echo "I definitely care about this file!" > my-project/IMPORTANT.TXT
cat my-project/IMPORTANT.txt

cd my-project/my-lib

# Specify (using a relative path) that I want to use my-lib as a modules folder, running inside of that folder
yarn add left-pad --modules-folder .

# Hey does my file exist?
cd ..
cat IMPORTANT.txt

Running this shows the yarn command failing, but IMPORTANT.txt having been deleted from the project folder. This does not occur if yarn includes this patch.

[arcanis]

I'm a bit wary of this change since it's technically breaking, but given that the current behavior is quite unexpected and proved dangerous in the wild I'm gonna go ahead and merge it as a bugfix. Hopefully I won't regret it later 😅

[arcanis]

Thanks!