Improve compat across node versions (#297)

Import Assertions were removed from Node v22 and replaced with Import Attributes. To be compatible with both, the simplest thing is to just use the filesystem APIs, even though they're more awkward.

Once everyone's on Node v22 or above, we can switch to using `import pkg from './package.json' with {type: 'json'};`

Author: rictic

.changeset/thirty-moons-count.md

@@ -0,0 +1,4 @@
+---
+---
+
+Internal change. Improve node version compatibility in the build script.

rollup.config.mjs

@@ -19,7 +19,17 @@ import replace from "rollup-plugin-replace";
 import typescriptPlugin from "rollup-plugin-typescript2";
 import typescript from "typescript";
 import json from "@rollup/plugin-json";
-import pkg from "./package.json" assert { type: "json" };
+import * as fs from "node:fs";
+import * as path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+// Once we drop support for Node versions <22 we can replace this line with
+// just:
+// import pkg from './package.json' with {type: 'json'};
+const pkg = JSON.parse(fs.readFileSync(path.join(__dirname, "package.json")));
 
 const es2017BuildPlugins = [
   typescriptPlugin({