chore: work around Ajv module bug in generated code (#256)

JavaScript module inconsistency strikes again.

In some cases, Ajv will inject `require` calls into generated code even
if you ask it to generate ESM. [This is a bug][0].

For example, here's something it adds if you use [the string `minLength`
or `maxLength` properties][1]:

    // ...
    const func2 = require("ajv/dist/runtime/ucs2length").default;
    // ...

That won't work in an ESM environment.

As a workaround, I inject the following into our generated code:

    import { createRequire } from 'node:module';
    const require = createRequire(import.meta.url);

This, along with moving `ajv` to production dependencies, should work
around this issue until the bug is fixed.

[0]: ajv-validator/ajv#2209
[1]: https://json-schema.org/understanding-json-schema/reference/string#length

package.json

@@ -42,7 +42,6 @@
     "@json-schema-tools/dereferencer": "^1.6.3",
     "@types/compact-encoding": "^2.15.0",
     "@types/json-schema": "^7.0.12",
-    "ajv": "^8.12.0",
     "c8": "^8.0.1",
     "cpy-cli": "^5.0.0",
     "eslint": "^8.46.0",
@@ -61,6 +60,7 @@
     "typescript": "^5.5.4"
   },
   "dependencies": {
+    "ajv": "^8.12.0",
     "compact-encoding": "^2.12.0",
     "protobufjs": "^7.2.5",
     "type-fest": "^4.26.0"

scripts/lib/generate-validations.js

@@ -26,5 +26,13 @@ export function generateValidations(config, jsonSchemas) {
   ajv.addKeyword('meta:enum')
 
   // generate validation code
-  return '// @ts-nocheck\n' + standaloneCode(ajv, schemaExports)
+  return [
+    '// @ts-nocheck',
+    // AJV has [a bug when generating ESM code][0]: it includes `require` in the
+    // output. We should be able to remove this once the bug is fixed.
+    // [0]: https://github.com/ajv-validator/ajv/issues/2209
+    "import { createRequire } from 'node:module';",
+    'const require = createRequire(import.meta.url);',
+    standaloneCode(ajv, schemaExports),
+  ].join('\n')
 }