Use custom is_printable instead of iswprint to fix emojis on OSX

If its good enough for musl, its likely good enough for us, and the
github issue shows that (at least some) terminal emulators do not
seem to rely on the libc iswprint in the first place.

Fixes #3059

Author: mawww

src/highlighters.cc

@@ -1230,6 +1230,13 @@ void highlight_selections(HighlightContext context, DisplayBuffer& display_buffe
 
 void expand_unprintable(HighlightContext context, DisplayBuffer& display_buffer, BufferRange)
 {
+    auto is_printable = [](Codepoint cp) { // follow musl iswprint set of printable characters, but with straightforward impl
+        if (cp < 0xff)
+            return cp == '\n' or cp >= ' ';
+        else if (cp == 0x2028 or cp == 0x2029 or (cp >= 0xFFF9 and cp <= 0xFFFB))
+            return false;
+        return true;
+    };
     const auto& buffer = context.context.buffer();
     auto error = context.context.faces()[FaceSpec{{}, "Error"}];
     for (auto& line : display_buffer.lines())
@@ -1245,7 +1252,7 @@ void expand_unprintable(HighlightContext context, DisplayBuffer& display_buffer,
             {
                 auto next = it;
                 Codepoint cp = utf8::read_codepoint(next, end);
-                if (cp != '\n' and (cp < ' ' or cp > '~') and not iswprint((wchar_t)cp))
+                if (not is_printable(cp))
                 {
                     if (ByteCount pos(it - line_data); pos != begin.column)
                         atom_it = ++line.split(atom_it, {begin.line, pos});