theme: make MUI v4 an optional peer dep

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/theme/package.json

@@ -34,14 +34,20 @@
   "dependencies": {
     "@emotion/react": "^11.10.5",
     "@emotion/styled": "^11.10.5",
-    "@material-ui/core": "^4.12.2",
     "@mui/material": "^5.11.2",
     "@mui/styles": "^5.11.2"
   },
   "peerDependencies": {
+    "@material-ui/core": "^4.12.2",
+    "@types/react": "^16.13.1 || ^17.0.0",
     "react": "^16.13.1 || ^17.0.0",
     "react-dom": "^16.13.1 || ^17.0.0"
   },
+  "peerDependenciesMeta": {
+    "@material-ui/core": {
+      "optional": true
+    }
+  },
   "devDependencies": {
     "@backstage/cli": "workspace:^",
     "@types/react": "^16.13.1 || ^17.0.0"

yarn.lock

@@ -9639,13 +9639,23 @@ __metadata:
     "@backstage/cli": "workspace:^"
     "@emotion/react": ^11.10.5
     "@emotion/styled": ^11.10.5
-    "@material-ui/core": ^4.12.2
     "@mui/material": ^5.11.2
     "@mui/styles": ^5.11.2
+<<<<<<< HEAD
+=======
+  peerDependencies:
+    "@material-ui/core": ^4.12.2
+>>>>>>> f1f6a256b36 (theme: make MUI v4 an optional peer dep)
     "@types/react": ^16.13.1 || ^17.0.0
   peerDependencies:
     react: ^16.13.1 || ^17.0.0
+<<<<<<< HEAD
     react-dom: ^16.13.1 || ^17.0.0
+=======
+  peerDependenciesMeta:
+    "@material-ui/core":
+      optional: true
+>>>>>>> f1f6a256b36 (theme: make MUI v4 an optional peer dep)
   languageName: unknown
   linkType: soft