chore: Simplify Babel config, inlining it Jest config

Author: eemeli

config/babel.config.js

@@ -1,9 +1,22 @@
 let moduleNameMapper
+
+const babel = [
+  'babel-jest',
+  {
+    overrides: [
+      {
+        test: '**/*.ts',
+        plugins: [
+          ['@babel/plugin-transform-typescript', { allowDeclareFields: true }]
+        ]
+      }
+    ],
+    presets: [['@babel/env', { targets: { node: 'current' } }]]
+  }
+]
+
 const transform = {
-  '[/\\\\]tests[/\\\\].*\\.(m?js|ts)$': [
-    'babel-jest',
-    { configFile: './config/babel.config.js' }
-  ]
+  '[/\\\\]tests[/\\\\].*\\.(m?js|ts)$': babel
 }
 
 // The npm script name is significant.
@@ -16,10 +29,7 @@ switch (process.env.npm_lifecycle_event) {
       '^yaml/util$': '<rootDir>/dist/util.js',
       '^../src/test-events$': '<rootDir>/dist/test-events.js'
     }
-    transform['[/\\\\]dist[/\\\\].*\\.mjs$'] = [
-      'babel-jest',
-      { configFile: './config/babel.config.js' }
-    ]
+    transform['[/\\\\]dist[/\\\\].*\\.mjs$'] = babel
     break
 
   case 'test':
@@ -30,10 +40,7 @@ switch (process.env.npm_lifecycle_event) {
       '^yaml/cli$': '<rootDir>/src/cli.ts',
       '^yaml/util$': '<rootDir>/src/util.ts'
     }
-    transform['[/\\\\]src[/\\\\].*\\.ts$'] = [
-      'babel-jest',
-      { configFile: './config/babel.config.js' }
-    ]
+    transform['[/\\\\]src[/\\\\].*\\.ts$'] = babel
 }
 
 module.exports = {

config/jest.config.js

@@ -16,7 +16,6 @@ export default {
     }),
     babel({
       babelHelpers: 'bundled',
-      configFile: './config/babel.config.js',
       presets: [['@babel/env', { modules: false }]]
     }),
     typescript({ declaration: false, outDir: 'browser/dist' })

config/rollup.browser-config.mjs

@@ -69,8 +69,6 @@
   },
   "devDependencies": {
     "@babel/core": "^7.12.10",
-    "@babel/plugin-transform-class-properties": "^7.23.3",
-    "@babel/plugin-transform-nullish-coalescing-operator": "^7.23.4",
     "@babel/plugin-transform-typescript": "^7.12.17",
     "@babel/preset-env": "^7.12.11",
     "@eslint/js": "^9.9.1",