chore(common): Backport FileTypeValidator fallback support to v10.4.17

[mag123c]

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

File validation fails when the buffer is too small or unidentifiable by magic number,
even if the mimetype is correct.

Related issue: #14977

What is the new behavior?

• Adds a fallbackToMimetype option to FileTypeValidator
• If magic number detection fails, and fallback is enabled, the validator uses the mimetype
• Also improves buildErrorMessage() for clearer failure messages

Does this PR introduce a breaking change?

• Yes
• No

Other information

This PR backports the fix originally merged in #14995 into the 10.4.17 line.

This was originally reported in #14977. All tests have been verified on the v10 codebase.

[mehdirayan]

Hi
i have an old code that no longer works after the upgrade.
i intercept the file like this:

@UseInterceptors(
FileInterceptor('photo', { dest: join(__dirname, '..', '/uploads') }),
)
@post()
async uploadeFile(
@uploadedfile(
new ParseFilePipe({
validators: [
new FileTypeValidator({ fileType: 'image/jpeg' }),
new MaxFileSizeValidator({ maxSize: 1024 * 100 }),
],
}),
)
file: Express.Multer.File,
)

The file is saved in the upload folder, so the buffer is missing in the file that is transmitted to validation.
The validation throw a type mismatch exception, with is confusing.

[mag123c]

@mehdirayan The issue for verifying the magic-number, the root cause of the issue, has not yet been resolved.

Check the issues below #14876, #14977, #15055