fix: Rename duplicate identifiers

[FrederikBolding]

Rename duplicate identifiers in test-snaps to prevent collisions during E2E.

---

Note

Low Risk
Test-harness DOM id changes only; no production or snap runtime behavior is affected.

Overview
Renames shared rpcResult DOM ids on the JSX and Preinstalled snap demo pages so each feature exposes a unique result span for tests.

Jsx.tsx now uses jsxResult; Preinstalled.tsx uses preinstalledResult. The JSON-RPC snap page keeps rpcResult, so E2E selectors no longer collide when multiple snap panels render on one page.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.59%. Comparing base (d4cf201) to head (bf73b1b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4069   +/-   ##
=======================================
  Coverage   98.59%   98.59%           
=======================================
  Files         428      428           
  Lines       12484    12484           
  Branches     1975     1975           
=======================================
  Hits        12309    12309           
  Misses        175      175           

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