[cmake] more modules, general "cleanup" (#3126)

Successor to that old MoltenVK PR. Does a lot of cleanups within root CMakeLists.txt, hands over MoltenVK and VulkanValidationLayers to CPMUtil, and separates out common operations into my modules.

Hopefully reduces the monstrosity that is root CMakeLists.txt. Please test:

- builds on all platforms
- VulkanValidationLayers

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3126
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

CMakeModules/GetSCMRev.cmake

@@ -1,49 +0,0 @@
-# SPDX-FileCopyrightText: 2025 crueter
-# SPDX-License-Identifier: GPL-3.0-or-later
-
-include(GetGitRevisionDescription)
-
-function(trim var)
-  string(REGEX REPLACE "\n" "" new "${${var}}")
-  set(${var} ${new} PARENT_SCOPE)
-endfunction()
-
-set(TAG_FILE ${CMAKE_SOURCE_DIR}/GIT-TAG)
-set(REF_FILE ${CMAKE_SOURCE_DIR}/GIT-REFSPEC)
-set(COMMIT_FILE ${CMAKE_SOURCE_DIR}/GIT-COMMIT)
-set(RELEASE_FILE ${CMAKE_SOURCE_DIR}/GIT-RELEASE)
-
-if (EXISTS ${REF_FILE} AND EXISTS ${COMMIT_FILE})
-  file(READ ${REF_FILE} GIT_REFSPEC)
-  file(READ ${COMMIT_FILE} GIT_COMMIT)
-else()
-  get_git_head_revision(GIT_REFSPEC GIT_COMMIT)
-  git_branch_name(GIT_REFSPEC)
-  if (GIT_REFSPEC MATCHES "NOTFOUND")
-    set(GIT_REFSPEC 1.0.0)
-    set(GIT_COMMIT stable)
-  endif()
-endif()
-
-if (EXISTS ${TAG_FILE})
-  file(READ ${TAG_FILE} GIT_TAG)
-else()
-  git_describe(GIT_TAG --tags --abbrev=0)
-  if (GIT_TAG MATCHES "NOTFOUND")
-    set(GIT_TAG "${GIT_REFSPEC}")
-  endif()
-endif()
-
-if (EXISTS ${RELEASE_FILE})
-  file(READ ${RELEASE_FILE} GIT_RELEASE)
-  trim(GIT_RELEASE)
-  message(STATUS "Git release: ${GIT_RELEASE}")
-endif()
-
-trim(GIT_REFSPEC)
-trim(GIT_COMMIT)
-trim(GIT_TAG)
-
-message(STATUS "Git commit: ${GIT_COMMIT}")
-message(STATUS "Git tag: ${GIT_TAG}")
-message(STATUS "Git refspec: ${GIT_REFSPEC}")