fix: open editor without inspector global

[pupuking723]

Fixes #824.

When the Vite plugin is detected, openInEditor() currently assumes window.__VUE_INSPECTOR__ has been registered. If the inspector runtime does not register that global, the "Open in Editor" action throws before it can reach the Vite open-in-editor middleware.

This keeps the existing inspector path when the global is available, and falls back to the same __open-in-editor?file=... request shape used by vite-plugin-vue-inspector when the global is missing.

Verification:

• pnpm exec vitest run packages/devtools-kit/__tests__/core/open-in-editor.test.ts --config /private/tmp/vue-devtools-vitest.config.ts
• pnpm exec eslint packages/devtools-kit/src/core/open-in-editor/index.ts packages/devtools-kit/__tests__/core/open-in-editor.test.ts
• pnpm build:devtools-kit
• git diff --check

I also tried pnpm type-check, but this checkout currently fails before reaching these files because packages/core/src/rpc/global.ts and packages/core/src/rpc/vite.ts cannot resolve hookable.

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[pupuking723]

I noticed #1098 covers the same missing-inspector case. The difference is that #1098 guards the call and warns, while this PR falls back to the Vite __open-in-editor endpoint and includes coverage for that path. I am happy to close this one or move the fallback and tests onto #1098 if that is easier to review.