[clr-ios] Update iOS on CoreCLR docs

[kotlarmilos]

Description

This PR updates the iOS on CoreCLR docs.

[dotnet-policy-service]

Tagging subscribers to 'os-ios': @vitek-karas, @kotlarmilos, @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

[davidnguyen-tech]

/ba-g Only a markdown file was updated.

[srxqds]

According to this document description, why is release build not supported yet?

[Copilot]

Pull Request Overview

This PR significantly expands and restructures the iOS on CoreCLR documentation, transforming it from a basic cross-compilation guide into comprehensive experimental support documentation. The changes improve documentation quality by adding detailed instructions, prerequisites, and troubleshooting information.

Key changes:

• Complete restructuring with table of contents and organized sections
• Addition of comprehensive build instructions for multiple iOS/tvOS platforms
• Enhanced sample app building and running instructions with debugging support

[kotlarmilos]

/ba-g markdown changes

[davidnguyen-tech]

/ba-g Only a markdown file was updated.

[davidnguyen-tech]

On my local machine, I've managed to verify that the instructions work on maccatalyst.

When running the HelloiOS app for iossimulator via command line, there's a tracking issue dotnet/xharness#1470 where a certain xharness version isn't able to create a simulator and the execution fails. However, when we run the HelloiOS app via Xcode, it works properly.