Remove CharKind::Newline

This is just a character, and so it seems clearer to refer to it specifically when we want to know if a character is a newline. There was only one case where we relied on Newline being different from Whitespace, and we special-cased that instance. Changing this actually makes us match the behavior of VS Code when double-clicking runs of multiple newlines.

/cc @as-cii

Co-Authored-By: Keith Simmons <keith@the-simmons.net>

crates/editor/src/multi_buffer.rs

@@ -1407,7 +1407,7 @@ impl MultiBufferSnapshot {
         );
 
         for ch in prev_chars {
-            if Some(char_kind(ch)) == word_kind {
+            if Some(char_kind(ch)) == word_kind && ch != '\n' {
                 start -= ch.len_utf8();
             } else {
                 break;
@@ -1415,7 +1415,7 @@ impl MultiBufferSnapshot {
         }
 
         for ch in next_chars {
-            if Some(char_kind(ch)) == word_kind {
+            if Some(char_kind(ch)) == word_kind && ch != '\n' {
                 end += ch.len_utf8();
             } else {
                 break;