Adds support for cwd in the git protocol (#6362)

## What's the problem this PR addresses?

The `git:` protocol supports cloning workspaces from a given repository,
but only if the project to install is at the root of the repository. It
may not be the case when the project contains libraries for multiple
languages.

## How did you fix it?

A new `cwd` parameter lets users pick a subpath to use when packing the
project. It can be used on its own, or in tandem with the `workspace`
specifier.

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Author: arcanis

.yarn/versions/40390280.yml

@@ -0,0 +1,25 @@
+releases:
+  "@yarnpkg/cli": minor
+  "@yarnpkg/plugin-git": minor
+
+declined:
+  - "@yarnpkg/plugin-compat"
+  - "@yarnpkg/plugin-constraints"
+  - "@yarnpkg/plugin-dlx"
+  - "@yarnpkg/plugin-essentials"
+  - "@yarnpkg/plugin-github"
+  - "@yarnpkg/plugin-init"
+  - "@yarnpkg/plugin-interactive-tools"
+  - "@yarnpkg/plugin-nm"
+  - "@yarnpkg/plugin-npm-cli"
+  - "@yarnpkg/plugin-pack"
+  - "@yarnpkg/plugin-patch"
+  - "@yarnpkg/plugin-pnp"
+  - "@yarnpkg/plugin-pnpm"
+  - "@yarnpkg/plugin-stage"
+  - "@yarnpkg/plugin-typescript"
+  - "@yarnpkg/plugin-version"
+  - "@yarnpkg/plugin-workspace-tools"
+  - "@yarnpkg/builder"
+  - "@yarnpkg/core"
+  - "@yarnpkg/doctor"

packages/acceptance-tests/pkg-tests-fixtures/repositories/deep-projects.git/HEAD

@@ -0,0 +1 @@
+ref: refs/heads/master

packages/acceptance-tests/pkg-tests-fixtures/repositories/deep-projects.git/config

@@ -0,0 +1,6 @@
+[core]
+	repositoryformatversion = 0
+	filemode = true
+	bare = true
+	ignorecase = true
+	precomposeunicode = true

packages/acceptance-tests/pkg-tests-fixtures/repositories/deep-projects.git/description

@@ -0,0 +1 @@
+Unnamed repository; edit this file 'description' to name the repository.

packages/acceptance-tests/pkg-tests-fixtures/repositories/deep-projects.git/info/exclude

@@ -0,0 +1,6 @@
+# git ls-files --others --exclude-from=.git/info/exclude
+# Lines that start with '#' are comments.
+# For a project mostly in C, the following would be a good set of
+# exclude patterns (uncomment them if you want to use them):
+# *.[oa]
+# *~

packages/acceptance-tests/pkg-tests-fixtures/repositories/deep-projects.git/info/refs

@@ -0,0 +1 @@
+a8499ffd064e21999185e9890fd60608785e4d42	refs/heads/master