Add a C API for tracked pins, known as a tracked grid ref in C.
The new API can create tracked refs from terminal points, snapshot them
back to regular grid refs for cell access, convert them to coordinates,
move them to a new point, report when their semantic location was lost,
and free the tracked pin bookkeeping. This is backed by PageList tracked
pins and exposed through the libghostty-vt export layer and headers.
Previously every file in the terminal package independently imported
build_options and ../lib/main.zig, then computed the same
lib_target constant. This was repetitive and meant each file needed
both imports just to get the target.
Introduce src/terminal/lib.zig which computes the target once and
re-exports the commonly used lib types (Enum, TaggedUnion, Struct,
String, checkGhosttyHEnum, structSizedFieldFits). All terminal
package files now import lib.zig and use lib.target instead of the
local lib_target constant, removing the per-file boilerplate.
Add a typed data query API to the terminal C interface, following
the same OutType pattern used by the OSC command data API. The new
ghostty_terminal_get function takes a GhosttyTerminalData tag and
an output pointer, returning GhosttyResult.
Currently exposes cols, rows, cursor x/y position, and cursor
pending wrap state. The GhosttyTerminalData enum is placed with the
other types in the header (before functions) per the ordering
convention.
