Revert "Revert "Limit GL_TEXTURE_RECTANGLE filtering to bilinear.""

This reverts commit ce4d04ae8eace6ba53ff8b8c8d8f4a2e6af4e59f.

BUG=skia:5932

Original CL description:
>
>Limit GL_TEXTURE_RECTANGLE filtering to bilinear.
>
>Adds a clamp for GrTexture filtering that can be set by a subclass at construction. The clamping is performed by GrTextureParams. GrGLTexture limits filtering to bilinear for rectangle and external textures.
>
>Also moves samplerType() to GrTexturePriv from GrTexture.
>
>BUG=skia:5932

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4455

Change-Id: I4a9f4abac44979cb900f5b04fe741524eade66b1
Reviewed-on: https://skia-review.googlesource.com/4455
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
10 files changed