meson: add support for the ImplictConversions option

meson.build

@@ -15,6 +15,8 @@ endif
 cpp_args = [
     '-DJSON_USE_GLOBAL_UDLS=@0@'.format(
         (not get_option('GlobalUDLs')).to_int()),
+    '-DJSON_USE_IMPLICIT_CONVERSIONS=@0@'.format(
+        (not get_option('ImplicitConversions')).to_int()),
 ]
 
 nlohmann_json_dep = declare_dependency(

meson_options.txt

@@ -10,3 +10,9 @@ option(
     value: true,
     description: 'Place user-defined string literals in the global namespace',
 )
+option(
+    'ImplicitConversions',
+    type: 'boolean',
+    value: true,
+    description: 'Enable implicit conversions',
+)