[iOS] Fix for the File.ContentType from MediaPicker not being in valid MIME format

[SyedAbdulAzeemSF4852]

Issue Details

• ContentType property from the file received after calling MediaPicker.PickPhotoAsync is not in the MIME format.

Root Cause

• Mapping the file extension to a MIME type is not done. The PlatformGetContentType method currently just returns the extension.

Description of Change

• UTType is only supported starting with iOS 14.0. Therefore If the application is running on iOS 14 or later, retrieved the Uniform Type Identifier (UTI) for a given file extension and obtained the associated PreferredMIMEType property of the Uniform Type Identifier. If a valid MIME type is found, assigned the MIME type to the file extension. Otherwise, returned the original file extension.
• src/Essentials/src/FileSystem/FileSystem.ios.tvos.watchos.macos.cs: Modified the PlatformGetContentType method to use UniformTypeIdentifiers.UTType.GetType for better MIME type resolution.

Validated the behaviour in the following platforms

• Windows
• Android
• iOS
• Mac

Issues Fixed

Fixes #15562

Output

Before	After
Before.mov	After.mov

[dotnet-policy-service]

Hey there @@SyedAbdulAzeemSF4852! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[FlavioGoncalves-Cayas]

Stumbled upon this issue and now this PR once again and wanted to adapt this solution myself.

I noticed that UTType is only supported starting with iOS 14.0. So this solution would crash on iOS versions <14.0.
AFAIK MAUI supports minimum iOS version of 12.2.

[jfversluis]

@SyedAbdulAzeemSF4852 why is this still a draft?

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

src/Essentials/test/DeviceTests/Tests/FileSystem_Tests.cs:57

• [nitpick] Consider wrapping the file deletion in a try-finally block to ensure the temporary file is always removed even if an assertion fails.

File.Delete(filePath);