Update remappings.txt for upgradeable contracts and set up submodule (#4639)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Ernesto García <ernestognw@gmail.com>

scripts/upgradeable/transpile-onto.sh

@@ -15,7 +15,7 @@ base="${2-}"
 bash scripts/upgradeable/transpile.sh
 
 commit="$(git rev-parse --short HEAD)"
-branch="$(git rev-parse --abbrev-ref HEAD)"
+start_branch="$(git rev-parse --abbrev-ref HEAD)"
 
 git add contracts
 
@@ -36,9 +36,19 @@ else
   fi
 fi
 
-# commit if there are changes to commit
-if ! git diff --quiet --cached; then
-  git commit -m "Transpile $commit"
+# abort if there are no changes to commit at this point
+if git diff --quiet --cached; then
+  exit
 fi
 
-git checkout "$branch"
+if [[ -v SUBMODULE_REMOTE ]]; then
+  lib=lib/openzeppelin-contracts
+  git submodule add -b "${base#origin/}" "$SUBMODULE_REMOTE" "$lib"
+  git -C "$lib" checkout "$commit"
+  git add "$lib"
+fi
+
+git commit -m "Transpile $commit"
+
+# return to original branch
+git checkout "$start_branch"

scripts/upgradeable/upgradeable.patch

@@ -319,6 +319,14 @@ index 3a1617c09..97e59c2d9 100644
    },
    "keywords": [
      "solidity",
+diff --git a/remappings.txt b/remappings.txt
+index 304d1386a..a1cd63bee 100644
+--- a/remappings.txt
++++ b/remappings.txt
+@@ -1 +1,2 @@
+-@openzeppelin/contracts/=contracts/
++@openzeppelin/contracts-upgradeable/=contracts/
++@openzeppelin/contracts/=lib/openzeppelin-contracts/contracts/
 diff --git a/test/utils/cryptography/EIP712.test.js b/test/utils/cryptography/EIP712.test.js
 index faf01f1a3..b25171a56 100644
 --- a/test/utils/cryptography/EIP712.test.js