fix: add Delphi/Pascal syntax highlighting support

[fbricon]

Description

#4771 was supposed to fix Pascal highlighting support but it actually removed Delphi support in the process. I'm just trying it again as I'm puzzled by the reason (delphi didn't exist according to tests).

Fixes #3586

Checklist

• I've read the contributing guide
• [] The relevant docs, if any, have been updated or created
• [] The relevant tests, if any, have been updated or created

Screenshots

Tests

• ask a chat model to write a "hello world" program in Pascal.
• pascal snippet should be highlighted.

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Summary by cubic

Restored Delphi/Pascal syntax highlighting support in the markdown preview so Pascal code snippets are highlighted correctly.

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[fbricon]

I suspect the "delphi didn't exist according to tests" statement might have been caused by referencing Delphi.js instead of delphi.js in the original commit, which would obviously fail when running on a case-sensitive OS (hello Linux)