Make `SelectionsCollection::disjoint_anchor_ranges` return an iterato… #39413

Job	Run time
Check Postgres and Protobuf migrations, mergability	10s
check_docs_only	18s
Check formatting and spelling	25s
(Linux) Build Remote Server	6s
(Linux) Run Clippy and tests	3s
(Windows) Run Clippy and tests	34s
(macOS) Run Clippy and tests	8s
Create a macOS bundle	0s
Create a Linux bundle	0s
Create arm64 Linux bundle	0s
Auto release preview	0s
	1m 44s

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