#989 Use Monaco Editor and save code in submitpage.php when edit the content

What does this PR aim to accomplish?:

Use Monaco Editor and save code in submitpage.php when edit the content.

How does this PR accomplish the above?:

Editor -> Monaco

Save code in localStorage.

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2. I have commented on my proposed changes within the code.
3. I have tested my changes.
4. I am willing to help maintain this change if there are issues with it later.
5. It is compatible with the GNU General Public License v3.0
6. I have squashed any insignificant commits. (git rebase)
7. I have checked that another pull request for this purpose does not exist.
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11. I have verified that my changes work correctly in both the new UI and the old/classic UI.

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Summary by Sourcery

Replace the legacy CodeMirror integration with a Monaco-based editor abstraction and apply it to the submission page, including autosave and graceful fallbacks.

New Features:

• Integrate Monaco editor loading and initialization utilities with a CodeMirror-compatible shim API.
• Use Monaco as the primary code editor on the submission page, including keyboard shortcuts and local code persistence per problem or contest.
• Show a small read-only Monaco code snippet (or text fallback) for generated freopen helper code in the error message area.

Bug Fixes:

• Harden editor sizing by providing a fixed minimum height fallback when automatic Monaco layout calculation fails.

Enhancements:

• Refine the submission page header structure for clearer dynamic rendering of problem or contest identifiers.

Build:

• Bump script and package version numbers to 3.5.2.

Summary by Sourcery

Replace the legacy CodeMirror integration with a Monaco-based editor abstraction and apply it to the submission page, including autosave and safer error/standard-solution displays.

New Features:

• Introduce a Monaco editor loader and CodeMirror-compatible shim used throughout the script.
• Use a Monaco-based editor on the submission page with per-problem local storage and keyboard shortcuts, falling back to a textarea if Monaco fails to load.
• Render a small read-only Monaco (or text) snippet for generated freopen helper code inside the error area.

Bug Fixes:

• Prevent CE info and standard-solution pages from breaking when the underlying page shows access-denied or missing-problem messages, and clean up any transient error snippet editors between submissions.

Enhancements:

• Refine the submission page header layout for clearer problem and contest identification and make editor sizing more robust, including viewport-fitting behavior.
• Align dark-mode themes across Monaco- and CodeMirror-based views by using the Monaco dark theme name where applicable.

Build:

• Bump userscript and package versions to 3.5.2 and update metadata for the new editor support.