Revert "refactored SkSLVarDeclaration out of existence"

This reverts commit 1ae353c887fdf447e1fe627e3cd29f8fa62c2a05.

Reason for revert: ASAN failures

Original change's description:
> refactored SkSLVarDeclaration out of existence
> 
> Bug: skia:
> Change-Id: I3dbc08e6d759f6828a472246d4797babb6cc132e
> Reviewed-on: https://skia-review.googlesource.com/66147
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

TBR=egdaniel@google.com,ethannicholas@google.com

Change-Id: I8cae451de1546fe783e32dd41df00eac7da61b21
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/68280
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
16 files changed