[Improvement] Add extended inclusion support for record types

[dulajdilshan]

Had offline chat with @sachiniSam on this. We thought of add two attributes to determine whether the fields are edited and from which type the fields are inherited from

• isIncludedField - a boolean, whether the particular field is inherited from another type (included type).
• includedIn - a type reference, the reference type which the field is inherited from.

Originally posted by @dulajdilshan in #539

[dulajdilshan]

Handled retrieving record types with type-inclusions. Need to work on creating record types with type-inclusion. PR: ballerina-platform/ballerina-language-server#276.

When creating the user will select the extending type and select the fields which he will change. Capturing this is bit tricky.
First, check whether the particular field's type and default value are changed from the original field. Then, generate the source code appropriately.