Update with an example HW selection guide and new use cases (#860)

This commit comprehensively updates the device selection explainer to reflect the latest discussions, API changes, and community feedback.

Key changes include:
- Updated Introduction and History sections to accurately reflect the removal of `MLDeviceType` from `MLContextOptions` (following PR #809) and the shift towards hint-based, implementation-led device selection.
- Clarified the impact of key issues (#749, #302, #350) and PRs (#809, #824, #855) on the device selection strategy.
- Ensured the "Key use cases and requirements" section aligns with the current API, incorporating the device preference use cases from PR #855.
- Updated JavaScript examples in "Scenarios, examples, design discussion" to be consistent with the current API, marking future/hypothetical features (like `opSupportLimitsPerDevice()` and a `fallback` option) with explanatory notes.
- Added new open questions based on recent discussions (e.g., issue #836, PR #854 regarding querying actual device usage).
- Refined the "Background thoughts" section, particularly the "Example Hardware Selection Guide," adding an editor's note about ongoing discussions (PR #860).
- Corrected the "Considered alternatives" and "Minimum Viable Solution" sections to accurately represent the current and past approaches.
- Updated the "Next Phase Device Selection Solution" to clarify the status of proposals like `querySupport` (issue #815) and the investigation of `graph.devices` (issue #836, PR #854).
- Performed a full proofread, correcting grammar, typos, and markdown formatting for improved clarity and consistency throughout the document.

Signed-off-by: Zoltan Kis <zoltan.kis@intel.com>
With thanks to Jules for proofreading:
Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: 2 people