Add internal `_degeneratize_R` and `_degeneratize_I` #670

Job	Run time
Documentation	8m 41s
Julia 1.6 - ubuntu-latest - x64 - pull_request	6m 57s
Julia 1.6 - macOS-latest - x64 - pull_request	7m 44s
Julia 1.6 - windows-latest - x64 - pull_request	12m 39s
Julia 1 - ubuntu-latest - x64 - pull_request	6m 35s
Julia 1 - macOS-latest - x64 - pull_request	5m 35s
Julia 1 - windows-latest - x64 - pull_request	9m 21s
Julia nightly - ubuntu-latest - x64 - pull_request	12m 2s
Julia nightly - macOS-latest - x64 - pull_request	8m 56s
Julia nightly - windows-latest - x64 - pull_request	11m 10s
	1h 29m 40s

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