[cmake] CPMUtil rewrite of the day number 852 (#4130)

Composite PR for several changes to CPMUtil, most notably:
- https://git.crueter.xyz/CMake/CPMUtil/pulls/19
- https://git.crueter.xyz/CMake/CPMUtil/pulls/22
- https://git.crueter.xyz/CMake/CPMUtil/pulls/24
- https://git.crueter.xyz/CMake/CPMUtil/pulls/25

These contain a lot of changes that generally simplify control flow and improve ease-of-use. Read those descriptions and patchsets for more info.

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4130
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

tools/cpm/cmake/package/which.cmake

@@ -0,0 +1,36 @@
+#!/usr/bin/env -S cmake -P
+
+# SPDX-FileCopyrightText: Copyright 2026 crueter
+# SPDX-License-Identifier: LGPL-3.0-or-later
+
+cmake_minimum_required(VERSION 3.31)
+
+include(${CMAKE_CURRENT_LIST_DIR}/../ScriptUtils.cmake)
+
+function(usage)
+    echo([=[
+Usage: cpmutil.sh package which [PACKAGE]...
+
+Check if a package or packages are defined in the cpmfile.
+]=])
+endfunction()
+
+set(NO_ALL TRUE)
+parse_script_args(args)
+set(exit 0)
+
+get_cpmfile_content(object)
+
+foreach(key ${args})
+    # Check if a key exists
+    string(JSON member ERROR_VARIABLE err GET "${object}" ${key})
+
+    if (NOT err)
+        echo("${key}")
+    else()
+        echo_error("${key} not defined in cpmfile")
+        set(exit 1)
+    endif()
+endforeach()
+
+cmake_language(EXIT ${exit})