Update to Yarn Modern

Yarn Classic was having some transient dependency/environment issues. Modern is... modern? And not broken.

*CHANGES*
- Migrated to Yarn Modern following documentation
- Added relevant ignores to `.gitignore` (Decided to forego zero install to keep checkout times down)
- Added `.gitattributes` to avoid `git diff` showing Yarn binary changes

.gitattributes

@@ -0,0 +1,3 @@
+# Don't show diffs of yarn releases etc.
+/.yarn/releases/** binary
+/.yarn/plugins/** binary

.gitignore

@@ -121,6 +121,16 @@ dist
 # production
 /build
 
+# yarn cruft
+## Disables zero install - https://yarnpkg.com/features/caching and https://yarnpkg.com/getting-started/qa#which-files-should-be-gitignored
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/sdks
+!.yarn/versions
+
 # misc
 .DS_Store
 .env.local

.yarnrc.yml

@@ -0,0 +1,3 @@
+nodeLinker: node-modules
+
+yarnPath: .yarn/releases/yarn-4.1.0.cjs

package.json

@@ -79,5 +79,6 @@
  "resolutions": {
  "@types/react": "17.0.25",
  "@types/react-dom": "17.0.25"
- }
+ },
+ "packageManager": "[email protected]"
 }