[core] GL performance fixes

[jfirebaugh]

Cherry-picks the following OpenGL performance and compatibility fixes to the release branch:

• [core] Reduce number of varyings to 8 or less #9251 -- Reduce number of varyings to 8 or less
• Store vertex attribute binding to prevent duplicate binds #9181 -- Store vertex attribute binding to prevent duplicate binds
• Dynamically compile shaders with uniforms instead of attributes for DDS #9185 -- Dynamically compile shaders with uniforms instead of attributes for DDS
• [core] Don't upload the FrameHistory texture in frames where it's not changing #9257 -- Don't upload the FrameHistory texture in frames where it's not changing

2017-06-13 12:17:58.318728-0700 Bench GL[7283:1811481] | paris      | 60.0 fps |
2017-06-13 12:17:58.318824-0700 Bench GL[7283:1811481] | paris2     | 60.0 fps |
2017-06-13 12:17:58.318910-0700 Bench GL[7283:1811481] | alps       | 60.2 fps |
2017-06-13 12:17:58.318992-0700 Bench GL[7283:1811481] | us east    | 60.1 fps |
2017-06-13 12:17:58.319074-0700 Bench GL[7283:1811481] | greater la | 60.1 fps |
2017-06-13 12:17:58.319212-0700 Bench GL[7283:1811481] | sf         | 60.1 fps |
2017-06-13 12:17:58.319564-0700 Bench GL[7283:1811481] | oakland    | 60.2 fps |
2017-06-13 12:17:58.319654-0700 Bench GL[7283:1811481] | germany    | 59.9 fps |
2017-06-13 12:17:58.319726-0700 Bench GL[7283:1811481] Total FPS: 480.6
2017-06-13 12:17:58.319797-0700 Bench GL[7283:1811481] Average FPS: 60.1

[jfirebaugh]

Don't review yet; I'm going to repurpose this PR to include the other GL performance fixes like #9185.

[zugaldia]

@jfirebaugh looks like Firebase was in a bad state, canceling the jobs and restarting them did the trick.

[jfirebaugh]

Thanks @zugaldia. This is now ready for review. @kkaefer could you post benchmark results from the iPad mini?

[boundsj]

Thanks @jfirebaugh @kkaefer. We can update the iOS release notes after this lands to note that there have been some performance fixes made under the hood.

[kkaefer]

0c275ad (current release branch tip)

name	Run 1	Run 2	Run 3
paris	17.2 fps	17.2 fps	17.2 fps
paris2	19.4 fps	18.5 fps	19.3 fps
alps	8.8 fps	8.9 fps	8.8 fps
us east	24.4 fps	25.6 fps	25.0 fps
greater la	17.6 fps	18.0 fps	18.0 fps
sf	22.5 fps	21.7 fps	21.6 fps
oakland	18.9 fps	19.3 fps	19.0 fps
germany	10.1 fps	10.3 fps	10.1 fps

this PR

name	Run 1	Run 2	Run 3
paris	47.6 fps	47.8 fps	47.6 fps
paris2	59.8 fps	59.9 fps	59.9 fps
alps	22.2 fps	22.2 fps	22.2 fps
us east	59.9 fps	59.8 fps	59.9 fps
greater la	47.4 fps	47.5 fps	47.5 fps
sf	60.1 fps	60.3 fps	60.3 fps
oakland	54.3 fps	54.2 fps	54.3 fps
germany	26.4 fps	26.4 fps	26.3 fps