feat(terminal): support OSC 52 to yank to system clipboard

Helper function for `App` which writes the necessary escape sequence
directly to yank the provided string.

examples/demo.zig

@@ -1,5 +1,5 @@
 const QuitText = struct {
-    const text = "Press ctrl+c to quit. Press ctrl+n to launch `vim`.";
+    const text = "Press ctrl+c to quit. Press ctrl+n to launch `vim`. Press space to yank to system clipboard.";
 
     pub fn element(this: *@This()) App.Element {
         return .{ .ptr = this, .vtable = &.{ .content = content } };
@@ -150,6 +150,12 @@ pub fn main(init: std.process.Init) !void {
             .key => |key| {
                 if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) try app.quit();
 
+                if (key.eql(.{ .cp = zterm.input.Space })) try app.yankToSystemClipboard(
+                    w,
+                    gpa,
+                    "This is a test of the OSC52 support:\n\tWith multiple lines and some special characters $?/-[]().╭─╮",
+                );
+
                 if (key.eql(.{ .cp = 'n', .mod = .{ .ctrl = true } })) {
                     try app.stop(w);
                     try w.flush();

src/app.zig

@@ -177,6 +177,11 @@ pub fn App(comptime M: type, comptime E: type) type {
             try this.queue.push(this.io, e);
         }
 
+        pub fn yankToSystemClipboard(this: *@This(), w: *std.Io.Writer, gpa: Allocator, str: []const u8) !void {
+            _ = this;
+            try terminal.yankToSystemClipboard(w, gpa, str);
+        }
+
         fn run(this: *@This()) !void {
             // thread to read user inputs
             var buf: [512]u8 = undefined;

src/terminal.zig

@@ -63,6 +63,17 @@ pub fn ringBell(w: *std.Io.Writer) !void {
     _ = try w.write(&.{7});
 }
 
+pub fn yankToSystemClipboard(w: *std.Io.Writer, gpa: Allocator, str: []const u8) !void {
+    const encoder: std.base64.Base64Encoder = .init(std.base64.url_safe_alphabet_chars, '=');
+    const encoded_str: []u8 = try gpa.alloc(u8, encoder.calcSize(str.len));
+    defer gpa.free(encoded_str);
+    _ = encoder.encode(encoded_str, str);
+    // NOTE for `tmux` support it should be configured to pass through the escape sequence for OSC52
+    const value = try std.fmt.allocPrint(gpa, ctlseqs.osc52_clipboard_copy, .{encoded_str});
+    defer gpa.free(value);
+    try w.writeAll(value);
+}
+
 pub fn read(buf: []u8) !usize {
     return try posix.read(posix.STDIN_FILENO, buf);
 }
@@ -227,6 +238,7 @@ const std = @import("std");
 const mem = std.mem;
 const posix = std.posix;
 const assert = std.debug.assert;
+const Allocator = mem.Allocator;
 const ctlseqs = @import("ctlseqs.zig");
 const input = @import("input.zig");
 const Key = input.Key;