expose parentContainer to templates

Description

I'm extending the models generated from swaggers with a deepCopy() method for java. For this I need to generate code based on the property types, but in case the basetype is List or Map, the detailed type information is lost to the templates.

I propose exposing the "parentContainer" type in these cases similar to how "items" are exposed for container properties.

The proof-of-concept code is ready, I'll file a PR soon.

Swagger-codegen version

2.4.10, 2.4.11-SNAPSHOT (HEAD)

Swagger declaration file content or url

swagger: "2.0"
info:
  version: "1.0.0"
  title: "test"

paths: {}

definitions:
  ArrType:
    type: array
    items:
      type: string
      format: date-time

Command line used for generation

java -jar ~/.m2/repository/io/swagger/swagger-codegen-cli/2.4.10/swagger-codegen-cli-2.4.10.jar generate -i testarr.yaml -l java -o /tmp/test -DdebugModels=true > logarr-orig.txt

java -jar ~/src/swagger-codegen/modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i testarr.yaml -l java -o /tmp/test -DdebugModels=true > logarr.txt

Steps to reproduce

N/A

Related issues/PRs

The PR will include the fix for #9918

Suggest a fix/enhancement

will file a PR

logarr-orig.txt
logarr.txt

Start with the Swagger definition in testarr.yaml and the Java CLI generation commands, then compare the attached debugModels outputs for the original and modified runs. Verify that generated templates can access parentContainer for List or Map properties and that Java generation still completes with the sample definition.