[ASTImporter][LLDB] Modifying ImportDeclContext(...) to ensure that we...

[ASTImporter][LLDB] Modifying ImportDeclContext(...) to ensure that we complete each FieldDecl of a RecordDecl when we are importing the definiton

This fix was motivated by a crashes in expression parsing during code generation in which we had a RecordDecl that had incomplete FieldDecl. During code generation when computing the layout for the RecordDecl we crash because we have several incomplete FieldDecl.

This fixes the issue by assuring that during ImportDefinition(...) for a RecordDecl we also import the definitions for each FieldDecl.

Differential Revision: https://reviews.llvm.org/D71378