range anchors: allow selecting when arriving on page with single-line anchor

[tleb]

• Click this link: https://elixir.bootlin.com/linux/v6.10.10/source/include/linux/pm.h#L62
• Shift+click L63.
• Current result: L63 is selected.
• (Possibly) expected behavior: L62-L63 are selected.

The JS stores previous clicks to know the current selection state. That means that when we land on a page with an anchor, our page's state doesn't contain the initial line as selected.

Can you confirm the proposed behavior is more intuitive? I did it without thinking when landing on the above page.