Unit tests for the live range conflict detection mechanism (CoalescedLiveRanges) in the Greedy Allocator.

Consolidated conflict detection and traversal logic in CoalescedLiveRanges to avoid duplication in both code and testing. In addition, this change achieves better separation between CoalescedLiveRanges and other register allocator components, improving testability and maintainability.

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Review URL: https://codereview.chromium.org/1219063017

Cr-Commit-Position: refs/heads/master@{#29783}