cmake_language: Rename command from cmake_command

Help/command/cmake_language.rst

Help/command/function.rst

Help/command/macro.rst

Help/manual/cmake-commands.7.rst

Help/release/dev/cmake_command-command.rst

Help/release/dev/cmake_language-command.rst

Source/CMakeLists.txt

Source/cmCMakeLanguageCommand.cxx

Source/cmCMakeLanguageCommand.h

Source/cmCommands.cxx

Tests/RunCMake/CMakeLists.txt

Tests/RunCMake/cmake_command/RunCMakeTest.cmake

...command_eval_extra_parameters_between_eval_and_code.cmake

...s/RunCMake/cmake_command/cmake_command_eval_message.cmake

...CMake/cmake_command/cmake_command_eval_no_code-stderr.txt

...s/RunCMake/cmake_command/cmake_command_eval_no_code.cmake

...cmake_command/cmake_command_eval_no_parameters-stderr.txt

...Make/cmake_command/cmake_command_eval_no_parameters.cmake

...command/cmake_command_eval_variable_outside_message.cmake

...make_command/cmake_command_invoke_double_evaluation.cmake