Add a CMake build

Tried to stay as close as possible to ja2_2019.sln

On Visual Studio 2022 just Project -> CMake Settings for Ja2, add
the x86 configurations you want and press F7.

Below shows how the -DLanguages -DApplications switches work, If you don't
set them, the CMakeCache.txt of them will be set to ENGLISH and JA2,
respectively:

cmake [...] // nothing set, configure just JA2_ENGLISH.exe by default
cmake [...] -DApplications="JA2UB" // configures just Unfinished Business
cmake [...] build -DApplications="JA2UB;JA2UBMAPEDITOR" // Unfinished Business and UB Map Editor
cmake [...] build -DApplications="JA2UB;JA2MAPEDITOR;ALL" // ALL is in the list, configures every application
cmake [...] build -DApplications="JA2MAPEDITOR;DeathStranding" // fatal error: DeathStranding not an application

cmake [...] -DLanguages="GERMAN" // configures just German targets
cmake [...] build -DLanguages="GERMAN;ENGLISH" // German and English
cmake [...] build -DLanguages="GERMAN;ENGLISH;ALL" // ALL is in the list, configures every language
cmake [...] build -DLanguages="ENGLISH;ESPERANTO" // fatal error: ESPERANTO not supported

cmake/ValidateOptions.cmake

@@ -0,0 +1,20 @@
+function(ValidateOptions ValidOptions ChoiceName DefaultChoice Choice RetVal)
+	if(Choice)
+		if(Choice MATCHES "ALL")
+			set(${RetVal} ${ValidOptions} PARENT_SCOPE)
+			message(STATUS "ALL ${ChoiceName} option set, configuring ${ValidOptions}.")
+		else()
+			foreach(x IN LISTS Choice)
+				if(x IN_LIST ValidOptions)
+					message(STATUS "Configuring for ${x}.")
+				else()
+					message(FATAL_ERROR "${x} not supported. The supported ${ChoiceName} are: ${ValidOptions}.")
+				endif()
+				set(${RetVal} ${Choice} PARENT_SCOPE)
+			endforeach()
+		endif()
+	else()
+		set(${RetVal} ${DefaultChoice} PARENT_SCOPE)
+		message(STATUS "No -D${ChoiceName}= parameter, configuring ${DefaultChoice} by default.")
+	endif()
+endfunction()