Add API to enable/disable auto-build of the DefaultRenderingPipeline.

[kircher1]

I use this to perform some custom setup after the DefaultRenderingPipeline is constructed; I construct the pipeline with auto-build disabled (to avoid it's ctor creating effects which will need to be recreated), then perform some setup, and finally prepare() and re-enable the pipeline's automaticBuild.

Prior to this change, I wasn't able to turn the automaticBuild back on so would have either had to track effect changes manually or live with unneeded effect creation in the ctor.

Other minor cleanup included.

[azure-pipelines]

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[azure-pipelines]

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