core: add function to get process info from the surface

This adds a function to the core surface to get process information
about the process(es) running in the terminal. Currently supported is
the PID of the foreground process and the name of the slave PTY.

If there is an error retrieving the information, or the platform does
not support retieving that information `null` is returned.

This will be useful in exposing the foreground PID and slave PTY name to
AppleScript or other APIs.

src/Surface.zig

@@ -6342,6 +6342,31 @@ fn testMouseSelectionIsNull(
     );
 }
 
+pub const ProcessInfo = enum {
+    /// The PID of the process that currently controls the PTY.
+    foreground_pid,
+    /// Gets the name of the slave PTY. Returned name points to an internal
+    /// buffer so it should not be modified or freed.
+    tty_name,
+
+    pub fn Type(comptime info: ProcessInfo) type {
+        return switch (info) {
+            .foreground_pid => u64,
+            .tty_name => [:0]const u8,
+        };
+    }
+};
+
+/// Get information about the process(es) running within the surface. Returns
+/// `null` if there was an error getting the information or the information is
+/// not available on a particular platform.
+pub fn getProcessInfo(self: *Surface, comptime info: ProcessInfo) ?ProcessInfo.Type(info) {
+    return switch (info) {
+        .foreground_pid => self.io.getProcessInfo(.foreground_pid),
+        .tty_name => self.io.getProcessInfo(.tty_name),
+    };
+}
+
 test "Surface: selection logic" {
     // We disable format to make these easier to
     // read by pairing sets of coordinates per line.