fix: correct textarea linebreaks in csv files

[lkssmnt]

Fix CSV export escaping and normalize field parsing in Request::download()

Changes:

• Replace semicolon joins with a robust csvLine() helper that correctly escapes delimiters, quotes and newlines.
• Normalize field values before CSV export
• Replace the inline parseField() function with a local closure $parseField for clearer scoping.
• Build header and rows using the new csvLine() helper to ensure correct escaping for all fields.

Why:

• The previous implementation used raw string joins (A::join([...], ';')) which failed to escape semicolons, quotes and embedded newlines inside field values. This produced invalid CSV when fields contained those characters or complex types (arrays/objects).
• The new approach ensures exports are RFC-compatible for common CSV readers and handles more data types reliably.

Testing / QA steps:

1. Create a form submission with:

• Fields containing semicolons and quotes
• Fields containing CRLF/newlines
• Array field values and nested objects (where applicable)
• Boolean and null values

2. Download the CSV via the existing UI/action that triggers Request::download().
3. Open and verify the exported CSV