Fix problem with detecting storage folder on windows

The `getFirstStoragePath()` method would break on windows:

```
Path contains invalid characters: /c:/git-repo/codespaces-codeql (codeQL.createSkeletonQuery)
```

This makes sense, since we're looking to get the parent folder by splitting for `/`.

In windows, paths use `\` instead of `/`.

So let's detect the platform and add a test for this case.

extensions/ql-vscode/src/skeleton-query-wizard.ts

@@ -104,7 +104,11 @@ export class SkeletonQueryWizard {
     // so we need to get the parent folder
     if (firstFolder.uri.path.includes("codeql-custom-queries")) {
       // slice off the last part of the path and return the parent folder
-      return firstFolder.uri.path.split("/").slice(0, -1).join("/");
+      if (process.platform === "win32") {
+        return firstFolder.uri.path.split("\\").slice(0, -1).join("\\");
+      } else {
+        return firstFolder.uri.path.split("/").slice(0, -1).join("/");
+      }
     } else {
       // if the first folder is not a ql pack, then we are in a normal workspace
       return firstFolder.uri.path;

extensions/ql-vscode/test/vscode-tests/cli-integration/skeleton-query-wizard.test.ts

@@ -305,7 +305,7 @@ describe("SkeletonQueryWizard", () => {
     it("should return the first workspace folder", async () => {
       jest.spyOn(workspace, "workspaceFolders", "get").mockReturnValue([
         {
-          name: "codeql-custom-queries-cpp",
+          name: "codespaces-codeql",
           uri: { path: "codespaces-codeql" },
         },
       ] as WorkspaceFolder[]);
@@ -347,6 +347,48 @@ describe("SkeletonQueryWizard", () => {
         expect(wizard.getFirstStoragePath()).toEqual("vscode-codeql-starter");
       });
     });
+
+    describe("if user is on windows", () => {
+      let originalPlatform: string;
+
+      beforeEach(() => {
+        originalPlatform = process.platform;
+        Object.defineProperty(process, "platform", {
+          value: "win32",
+        });
+      });
+
+      afterEach(() => {
+        originalPlatform = process.platform;
+        Object.defineProperty(process, "platform", {
+          value: originalPlatform,
+        });
+      });
+
+      it("should return the first workspace folder", async () => {
+        jest.spyOn(workspace, "workspaceFolders", "get").mockReturnValue([
+          {
+            name: "codespaces-codeql",
+            uri: { path: "codespaces-codeql\\codeql-custom-queries-cpp" },
+          },
+        ] as WorkspaceFolder[]);
+
+        Object.defineProperty(process, "platform", {
+          value: "win32",
+        });
+
+        wizard = new SkeletonQueryWizard(
+          mockCli,
+          jest.fn(),
+          credentials,
+          extLogger,
+          mockDatabaseManager,
+          token,
+        );
+
+        expect(wizard.getFirstStoragePath()).toEqual("codespaces-codeql");
+      });
+    });
   });
 
   describe("findDatabaseItemByNwo", () => {