If the path is too long to fit on the screen, this patch makes it so
we elide the first part of it. It goes a bit further and trims it down
to ~70% of the screen, giving some room for the stat. This seems
somewhat similar to what Git does.
`insta` ignores leading indentation (as long as it's consistent within
the snapshot), but when a test case fails and you let `cargo insta`
update it, it's going to use a specific indentation. There were a few
tests that didn't match that indentation, which could lead to
surprising diffs if the tests fail at some point.
This shows that there's too much padding because we pad based on
number of bytes.
I had to reduce the path names for the file names not to get too long
for my file system.
We can still crash on terminals that are less than 4 characters wide
(maybe it doesn't matter if we do because the user can't tell the
crash report from a diffstat in such a terminal?). This patch fixes
the crash.
We would run into a panic due to "attempt to subtract with overflow"
if the path was long. This patch fixes that and adds tests showing the
current behavior when there are long paths and/or large diffs.
I've extracted the `builtin_log_root` template for users to customize the
default templates without fully overriding them, for example I would remove
the change_id/commit_id for myself - and we discussed in Discord that leaving
those makes sense for the user to be reminded/teached that the root commit has
a change id made from z's.
Empty files can be confusing in diff output. For example:
```
Added regular file file1:
Added regular file file2:
1: foo
```
This commit adds an "(empty)" placeholder instead. Since it's not
colored, and doesn't have line numbers, it will hopefully not be
mistaken for a file with the contents "(empty)".
