Don't add artificial newline to last line if --style=plain

This fixes #1438.

Note however, that using a pager such as less will add a newline itself.
So to actually not print a newline for such files, you need to either
disable paging:

  bat --style=plain --paging=never no-newline-at-end-of-file.txt

or use a "pager" that does not add a newline:

  bat --style=plain --pager=cat no-newline-at-end-of-file.txt

Note that we also update syntax tests file since a bunch of them had
missing newlines on the last lines.

CHANGELOG.md

@@ -5,6 +5,8 @@
 
 ## Bugfixes
 
+- If the last line doesn't end with a newline character, don't add it if `--style=plain`, see #1438 (@Enselic)
+
 ## Other
 
 ## Syntaxes

src/printer.rs

@@ -460,7 +460,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
                 }
             }
 
-            if line.bytes().next_back() != Some(b'\n') {
+            if !self.config.style_components.plain() && line.bytes().next_back() != Some(b'\n') {
                 writeln!(handle)?;
             }
         } else {

tests/syntax-tests/highlighted/Plaintext/plaintext.txt

@@ -175,4 +175,4 @@
 \u{ad}␊
 \u{ae}␊
 ␊
-Here's·a·line·with·multiple·characters.
+Here's·a·line·with·multiple·characters.␊