fix(auto_pairs): fix auto pairs with crlf

Auto pairs were resulting in incorrect ranges in the resulting when the
line terminators are CRLF (i.e. Windows). It turns out this is because
when we were checking if the selection was a single-width cursor, it
incorrectly assumed that this would be a single char. This is not the
case, as a cursor can cover a multi-code point grapheme. Therefore,
we must instead explicitly work with and check graphemes to determine
if the cursor should move or extend the selection.

Fixes #1436

helix-core/Cargo.toml

@@ -41,3 +41,5 @@ chrono = { version = "0.4", default-features = false, features = ["alloc", "std"
 
 [dev-dependencies]
 quickcheck = { version = "1", default-features = false }
+fern = "0.6"
+chrono = { version = "0.4", default-features = false, features = ["clock"] }