cmake.eclass: New eclass, EAPI-7 only cleanup of cmake-utils

cmake.eclass: New eclass, EAPI-7 only cleanup of cmake-utils

- Drop all pre-EAPI-7 compatibility
- Drop CMAKE_MIN_VERSION
- Drop CMAKE_REMOVE_MODULES
- Array support for CMAKE_REMOVE_MODULES_LIST
- Drop pushd/popd from src_prepare
- Drop _cmake_generator_to_use()
  CMAKE_MAKEFILE_GENERATOR validity is already checked in global scope.
  Move the check for dev-util/ninja into src_prepare.
- Rename cmake_src_make() -> cmake_build()
- Drop _cmake_ninja_src_build and _cmake_emake_src_build, move into cmake_build

Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>