Problem:
The default 'ruler' is implemented in C instead of the 'statusline' DSL.
Solution:
Replace the C implementation with a default 'rulerformat' expression.
This is a continuation of #1248 and #33036.
Advantages:
- configuration is more discoverable, the default being a useful example
- users and plugins can augment the default
- code reuse and less C code to maintain
- ui2: due to the use of an item group with `minwid`, it can expand
instead of truncating when the content gets too long, which is
particularly useful for locales with long translations of Top/Bot/All
Implementation details:
As is the case for 'statusline', when trying to set 'rulerformat' to an
empty string, the default expression is restored instead, mimicking how
previously the default C implementation would have been activated.
Just like before, `:set rulerformat=` and `:set rulerformat&` have the
same effect, and the ruler is disabled with `:set noruler`.
The default expression uses an item group with `%=`, unlike the fallback
in the previous default statusline `%-14.(%l,%c%V%) %P`, because the
total width and how it is configured is immediately clear without
documentation, it is a more useful pattern in general that works when
both sides have flexible width, and it also works for vim, which is
useful for configuration sharing/reuse.
A truncation marker `%<` is added at the end to mimic how at small
screen widths, the scroll percentage would disappear first, so that the
cursor position can remain fully visible.
BREAKING CHANGES:
- `&rulerformat` can no longer be set to an empty string
- ui2: the default ruler is no longer of fixed width, but can expand
- at very small screen widths (< 36 columns)
- ui2: it will no longer try to shrink white-space before truncating
- it truncates gradually from the right, whereas previously, the
scroll percentage would disappear all at once
- l10n can no longer add a space after the comma between line and column
(this was only done for one language: Ukrainian)
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