👷(vitest) Move build chain to ESM

The build chain of `@fast-check/vitest` has been CommonJS-based since day 1. With ESM moving forward in the ecosystem, it's time to move ourselves to the new standard and adapt our build chains to ESM.

Unfortunately it may have some subtle impacts on our users as our package will not be a CJS one offering a ESM fallback anymore. I will rather be the opposite: an ESM package with a fallback to CJS. It implies that we moved ESM related files closer to the root of the package (we could have kept them in esm/) and moved the CJS ones further in the file structure (we had to move them).

Another subtle impact is that it would impose our users to run at least Node ≥12.17.0. But it was already a requirement for this package.

As such we consider it as a breaking change.

packages/vitest/package.cjs-template.json

@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}

packages/vitest/package.json

@@ -2,33 +2,33 @@
   "name": "@fast-check/vitest",
   "description": "Property based testing for Vitest based on fast-check",
   "version": "0.0.9",
-  "type": "commonjs",
+  "type": "module",
   "main": "lib/vitest-fast-check.js",
   "exports": {
     "./package.json": "./package.json",
     ".": {
       "require": {
-        "types": "./lib/vitest-fast-check.d.ts",
-        "default": "./lib/vitest-fast-check.js"
+        "types": "./lib/cjs/vitest-fast-check.d.ts",
+        "default": "./lib/cjs/vitest-fast-check.js"
       },
       "import": {
-        "types": "./lib/esm/vitest-fast-check.d.ts",
-        "default": "./lib/esm/vitest-fast-check.js"
+        "types": "./lib/vitest-fast-check.d.ts",
+        "default": "./lib/vitest-fast-check.js"
       }
     }
   },
-  "module": "lib/esm/vitest-fast-check.js",
+  "module": "lib/vitest-fast-check.js",
   "types": "lib/vitest-fast-check.d.ts",
   "files": [
     "lib"
   ],
   "scripts": {
     "build": "yarn build:publish-cjs && yarn build:publish-esm && yarn build:publish-types",
     "build-ci": "yarn build",
-    "build:publish-types": "tsc -p tsconfig.publish.types.json && tsc -p tsconfig.publish.types.json --outDir lib/esm",
-    "build:publish-cjs": "tsc -p tsconfig.publish.json",
-    "build:publish-esm": "tsc -p tsconfig.publish.json --module es2015 --moduleResolution node --outDir lib/esm && cp package.esm-template.json lib/esm/package.json",
-    "test": "jest",
+    "build:publish-types": "tsc -p tsconfig.publish.types.json && tsc -p tsconfig.publish.types.json --outDir lib/cjs",
+    "build:publish-cjs": "tsc -p tsconfig.publish.json --outDir lib/cjs && cp package.cjs-template.json lib/cjs/package.json",
+    "build:publish-esm": "tsc -p tsconfig.publish.json --module es2015 --moduleResolution node",
+    "test": "yarn node --experimental-vm-modules $(yarn bin jest)",
     "test-bundle": "node test-bundle/basic.mjs && vitest --config test-bundle/vitest.config.mjs",
     "typecheck": "tsc --noEmit"
   },