Use simple lookup table for replacements in `StubbedMock` #2396

Job	Run time
Test coverage	23s
Confirm config and documentation	10s
Edge RuboCop: internal_investigation	13s
Oldest RuboCop: spec	17s
Edge RuboCop: spec	21s
Prism	30s
Ruby 2.7: internal_investigation	26s
RSpec 4	20s
Ruby 2.7: spec	30s
Ruby 3.0: internal_investigation	11s
Ruby 3.0: spec	22s
Ruby 3.1: internal_investigation	11s
Ruby 3.1: spec	20s
Ruby 3.2: internal_investigation	10s
Ruby 3.2: spec	21s
Ruby 3.3: internal_investigation	15s
Ruby 3.3: spec	21s
Ruby ruby-head: internal_investigation	17s
Ruby ruby-head: spec	17s
Ruby jruby-9.4: internal_investigation	1m 18s
Ruby jruby-9.4: spec	1m 22s
	8m 35s

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