renderer: don't constrain Powerline glyphs

This adds the Powerline glyphs to the exemptions from the PUA
constraints put in as a part of #1110.

While Powerline is considered to part of the Nerd Font group, the
constraint behavior seems to cause issues with some setups - e.g.
powerlevel10k prompts where characters immediately follow a Powerline
character.

Only the codes given as shapes below are included:
  https://github.com/ryanoasis/powerline-extra-symbols/blob/master/img/fontforge.png

Fixes #1113, where the issue can be seen.

src/renderer/cell.zig

@@ -45,6 +45,12 @@ pub fn fgMode(
                 break :text .normal;
             }
 
+            // We exempt the Powerline range from this since they exhibit
+            // box-drawing behavior and should not be constrained.
+            if (isPowerline(cell.char)) {
+                break :text .normal;
+            }
+
             // If we are at the end of the screen its definitely constrained
             if (x == screen.cols - 1) break :text .constrained;
 
@@ -69,3 +75,11 @@ pub fn fgMode(
         },
     };
 }
+
+// Returns true if the codepoint is a part of the Powerline range.
+fn isPowerline(char: u32) bool {
+    return switch (char) {
+        0xE0B0...0xE0C8, 0xE0CA, 0xE0CC...0xE0D2, 0xE0D4 => true,
+        else => false,
+    };
+}