Link hints: when opening a link in a new tab, ignore if shift is pressed

I wanted to raise the idea of a change to how shift-F (open link hints in new tab) works.

Over the years there have been many bug reports about show shift-F is not working as people expect, so it must have some confusing properties.

The feature's behavior is:

1. "f" launches a mode which opens a selected hint in the current tab. If shift is held while typing a link hint, the link will open in a new tab.
2. "F" does the same, except links will open in a new tab. However, if shift is held when typing a hint, the link will open in the current tab.

Most of the confusion happens because the link letters are shown as capitals, and so some people mistakenly type them as capitals (using shift). People eventually figure this out, and I don't have any idea for improving it anyway. See #4307, #4279, #3070, #1928, #1876, #761.

I think adding to the confusion is how shift is handled in case number 2: even if you type shift-F, the link may still open in the second tab if you type a capital hint. I think that's unnecessary and confusing, and I'd like to consider removing that functionality.

If anyone uses this feature and strongly objects, or has other ideas for decreasing the confusion, please chime in.

The issue names no files or tests; start by locating the link-hint handling for f/F and modifier-key processing, then inspect any existing tests. Done means Shift-F opens the selected link in a new tab without changing that behavior when a capital hint is entered.