refactor: add func getNlsConfiguration & tests

This PR refactors part of vscode.ts and adds a function to get the NLS
Configuration.

This makes the code more readable and easier to test.

And it adds multiple tests for this part of the codebase.

test/unit/browser/vscode.test.ts

@@ -0,0 +1,61 @@
+/**
+ * @jest-environment jsdom
+ */
+import { JSDOM } from "jsdom"
+import { getNlsConfiguration, nlsConfigElementId } from "../../../src/browser/pages/vscode"
+
+describe("vscode", () => {
+  describe("getNlsConfiguration", () => {
+    beforeEach(() => {
+      const { window } = new JSDOM()
+      global.document = window.document
+    })
+
+    it("should throw an error if Document is undefined", () => {
+      const errorMsgPrefix = "[vscode]"
+      const errorMessage = `${errorMsgPrefix} Could not parse NLS configuration. document is undefined.`
+
+      expect(() => {
+        getNlsConfiguration(undefined as any as Document)
+      }).toThrowError(errorMessage)
+    })
+    it("should throw an error if no nlsConfigElement", () => {
+      const errorMsgPrefix = "[vscode]"
+      const errorMessage = `${errorMsgPrefix} Could not parse NLS configuration. Could not find nlsConfigElement with id: ${nlsConfigElementId}`
+
+      expect(() => {
+        getNlsConfiguration(document)
+      }).toThrowError(errorMessage)
+    })
+    it("should throw an error if no nlsConfig", () => {
+      const mockElement = document.createElement("div")
+      mockElement.setAttribute("id", nlsConfigElementId)
+      document.body.appendChild(mockElement)
+
+      const errorMsgPrefix = "[vscode]"
+      const errorMessage = `${errorMsgPrefix} Could not parse NLS configuration. Found nlsConfigElement but missing data-settings attribute.`
+
+      expect(() => {
+        getNlsConfiguration(document)
+      }).toThrowError(errorMessage)
+
+      document.body.removeChild(mockElement)
+    })
+    it("should return the correct configuration", () => {
+      const mockElement = document.createElement("div")
+      const dataSettings = {
+        first: "Jane",
+        last: "Doe",
+      }
+
+      mockElement.setAttribute("id", nlsConfigElementId)
+      mockElement.setAttribute("data-settings", JSON.stringify(dataSettings))
+      document.body.appendChild(mockElement)
+      const actual = getNlsConfiguration(global.document)
+
+      expect(actual).toStrictEqual(dataSettings)
+
+      document.body.removeChild(mockElement)
+    })
+  })
+})