Re: [PATCH v3 1/5] commit: clarify FROM_REBASE_PICK and is_from_rebase() names

"Elijah Newren via GitGitGadget" [off-list ref] writes:

From: Elijah Newren <redacted>

Commit 430b75f7209c (commit: give correct advice for empty commit during
a rebase, 2019-12-06) introduced a FROM_REBASE_PICK enum value and an
is_from_rebase() function.  Those names failed to convey that they were
specifically about hitting a commit that becomes empty when rebasing.
Clarify their names now.

Becomes empty is different from picking an empty commit, right.  I
am not sure if "is_from_rebase_empty()" conveys the difference and
more importantly, I am afraid it hints the latter.  I have a feeling
that EMPTY_REBASE (instead of REBASE_EMPTY) may match what we want
to express slightly better, but not by a large margin to make a
difference.  Perhaps Phillip has a better idea?

While at it, change `whence == FROM_REBASE_EMPTY` to use
`is_from_rebase_empty(whence)`.

Very much appreciated.