Designer simplification - replace MethodArgument by ArgumentContent

[openlowcode]

In Open Lowcode designer, The MethodArgument method does not seem to add any value compared to the ArgumentContent class.

Method Argument should be replaced everywhere by ArgumentContent. This will not impact the code of applications generated with Open Lowcode designer, just property definition in Open Lowcode designer.

Both classes are part of org.openlowcode.design.data.