Config: cursor-style can bet set to block_hollow

`cursor-style` can now also be set to `block_hollow`, no other changes
in behaviour are added.

src/config/Config.zig

@@ -325,6 +325,7 @@ palette: Palette = .{},
 ///   * `block`
 ///   * `bar`
 ///   * `underline`
+///   * `block_hollow`
 ///
 @"cursor-style": terminal.CursorStyle = .block,
 

src/renderer/cursor.zig

@@ -16,6 +16,7 @@ pub const CursorStyle = enum {
         return switch (style) {
             .bar => .bar,
             .block => .block,
+            .block_hollow => .block_hollow,
             .underline => .underline,
         };
     }

src/terminal/Screen.zig

@@ -139,7 +139,7 @@ pub const Cursor = struct {
 /// The visual style of the cursor. Whether or not it blinks
 /// is determined by mode 12 (modes.zig). This mode is synchronized
 /// with CSI q, the same as xterm.
-pub const CursorStyle = enum { bar, block, underline };
+pub const CursorStyle = enum { bar, block, underline, block_hollow };
 
 /// Saved cursor state.
 pub const SavedCursor = struct {

src/termio/stream_handler.zig

@@ -208,6 +208,7 @@ pub const StreamHandler = struct {
                         const blink = self.terminal.modes.get(.cursor_blinking);
                         const style: u8 = switch (self.terminal.screen.cursor.cursor_style) {
                             .block => if (blink) 1 else 2,
+                            .block_hollow => if (blink) 1 else 2,
                             .underline => if (blink) 3 else 4,
                             .bar => if (blink) 5 else 6,
                         };