input configuration to pass input as stdin on startup

This adds a new configuration `input` that allows passing either raw
text or file contents as stdin when starting the terminal.

The input is sent byte-for-byte to the terminal, so control characters
such as `\n` will be interpreted by the shell and can be used to run
programs in the context of the loaded shell.

Example: `ghostty --input="hello, world\n"` will start the your default
shell, run `echo hello, world`, and then show the prompt.

src/config/string.zig

@@ -3,7 +3,7 @@ const std = @import("std");
 /// Parse a string literal into a byte array. The string can contain
 /// any valid Zig string literal escape sequences.
 ///
-/// The output buffer never needs sto be larger than the input buffer.
+/// The output buffer never needs to be larger than the input buffer.
 /// The buffers may alias.
 pub fn parse(out: []u8, bytes: []const u8) ![]u8 {
     var dst_i: usize = 0;