Claude review: drm/damage-helper: Test src coord in drm_atomic_helper_check_plane_damage()

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Correctness**: This moves the `drm_rect_equals(&state->src, &old_state->src)` check from `drm_atomic_helper_damage_iter_init()` (commit time) to `drm_atomic_helper_check_plane_damage()` (check time). This is the right place for it because:
- The check requires the old plane state, which should be available during atomic_check but shouldn't need to be threaded through to commit-time helpers.
- Setting `ignore_damage_clips` at check time gives a consistent view to all downstream consumers.

The function signature changes from `(state, plane_state)` to `(state, old_plane_state, new_plane_state)` which is consistent.

**Test removals**: 6 tests are dropped (`*_src_moved`, `*_fractional_src_moved`, `*_damage_not_visible` with src moved). This is appropriate because those tests were testing the src-comparison logic inside `damage_iter_init`, which no longer exists there. The `drm_test_damage_iter_damage_ignore` test from patch 1 covers the equivalent behavior via the flag.

However, I note the `drm_test_damage_iter_damage_not_visible` test is also removed here. This test had `mock->state.visible = false` *and* moved src coords. The `visible = false` case is still covered by the existing `drm_test_damage_iter_no_damage_not_visible` test (which doesn't move src), so no coverage gap.

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