Rework diff rendering to allow putting the cursor into deleted text, soft-wrapping and scrolling deleted text correctly #39906

Job	Run time
check_docs_only	19s
Check Postgres and Protobuf migrations, mergability	14s
Check formatting and spelling	4s
(Linux) Run Clippy and tests	2m 39s
(macOS) Run Clippy and tests	15s
(Windows) Run Clippy and tests	4m 17s
(Linux) Build Remote Server	2m 8s
Create a macOS bundle	0s
Create a Linux bundle	0s
Create arm64 Linux bundle	0s
Auto release preview	0s
	9m 56s

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