… VimModeSettings" (#44960)

Reverts #44889

Release Notes:
- N/A

…Settings (zed-industries#44889)

In a previous Pull Request, a new field was added to `editor::Editor`,
namely `cursor_offset_on_selection`, in order to control whether the
cursor representing the head of a selection should be positioned in the
last selected character, as we have on Vim mode, or after, like we have
when Vim mode is disabled.

This field would then be set by the `vim` crate, depending on the
current vim mode. However, it was noted that
`vim_mode_setting::VimModeSetting` already exsits and allows other
crates to determine whether Vim mode is enabled or not. Since we're
already checking `!range.is_empty()` in
`editor::element::SelectionLayout::new` we can then rely on simply
determining whether Vim mode is enabled to decide whether tho shift the
cursor one position to the left when making a selection.

As such, this commit removes the `cursor_offset_on_selection` field, as
well as any related methods in favor of a new `Editor.vim_mode_enabled`
method, which can be used to achieve the same behavior.

Relates to zed-industries#42837 

Release Notes:

- N/A

… VimModeSettings" (zed-industries#44960)

Reverts zed-industries#44889

Release Notes:
- N/A

zed-industries#44889 added the
`cursor_offset_on_selection` field, which displays the cursor *after* the
end of the selection unless a vim visual mode is enabled, in which case
it gets displayed *at* the end of the selection.

However, the real helix is effectively *always* in select mode, and
will always display the cursor at the end of the selection, whether that
selection is made via its visual mode, a movement key, or with the mouse.

This makes it so that the helix mode setting is taken into account
regardless of the visual-ness of the vim mode in the `sync_vim_settings`
method.