[ci] Fix helix local

[rmarinho]

Description of Change

Small fixes to be able to run locally, and improve documentation

This pull request updates the documentation and build configuration for running device tests locally and sending them to Helix. The main improvements clarify the setup steps, correct build commands, and introduce required environment variables for Helix integration.

Documentation improvements:

• Added a note specifying that commands should be run from the root of the maui repository to avoid confusion.
• Clarified the build command for MSBuild tasks by using $(PWD) to ensure the correct project path is used.
• Added instructions to export required environment variables for Helix, with a reference to more detailed documentation.

Build configuration updates:

• Set the TargetsAppleMobile property when targeting iOS, which helps configure Helix for Apple mobile platforms.
• Moved the conditional setting of TargetsAppleMobile to avoid duplication and ensure it only applies when the access token is not empty.

[Copilot]

Pull Request Overview

This PR fixes issues with running Helix device tests locally and improves the documentation. The changes include correcting build commands, adding required environment variables, and reorganizing build configuration properties.

Key changes:

• Fixed documentation with proper build command syntax using $(PWD) for correct project paths
• Added required environment variables setup for Helix integration
• Reorganized build configuration to conditionally set properties based on access tokens

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
eng/helix_xharness.proj	Moved and reorganized property settings for better conditional logic
docs/DevelopmentTips.md	Added clarifications and environment variable setup instructions