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.

tests/syntax-tests/source/Batch/build.bat

@@ -56,4 +56,4 @@ set LDLIBS= ^
     @set "LINK_FILES=%LINK_FILES% %%~f"
 )
 
-lld-link.exe %LINK_FILES% -out:"%OUTPUT%" %LDFLAGS% %LDLIBS%
+lld-link.exe %LINK_FILES% -out:"%OUTPUT%" %LDFLAGS% %LDLIBS%