fix: CompositeCanvasRenderer not supporting RectMask2D

[hatayama]

Description

• Fixed an issue where CompositeCanvasRenderer was not compatible with RectMask2D component

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as
  expected)
• Update documentations
• Others (refactoring, style changes, etc.)

Test environment

• Platform: Editor(Windows/Mac), Standalone(Windows/Mac)
• Unity version: 2019.4+

Checklist

• [ x] This pull request is for merging into the develop branch
• [ x] My code follows the style guidelines of this project
• [ x] I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• [ x] My changes generate no new warnings
• [ x] I have checked my code and corrected any misspellings