feat(language-server): extract find-fn-line from go-to-action

packages/language-server/helpers/find-fn-line.js

@@ -0,0 +1,21 @@
+const fs = require('fs').promises
+const url = require('url')
+
+module.exports = async function findFnLine(filePath) {
+  try {
+    const resolvedPath = filePath.startsWith('file:')
+      ? url.fileURLToPath(filePath)
+      : filePath
+
+    const content = await fs.readFile(resolvedPath, 'utf8')
+    const lines = content.split('\n')
+    for (let i = 0; i < lines.length; i++) {
+      if (lines[i].includes('fn:')) {
+        return i // Return the line number (0-based index)
+      }
+    }
+    return 0 // If 'fn:' is not found, return the first line
+  } catch (error) {
+    return 0 // Return the first line if there's an error
+  }
+}