Replace ._transform with public method to evaluate all the preprocessing steps of a pipeline

[angela97lin]

Closes #1225

API reference here: https://evalml.alteryx.com/en/1225_public_pipeline_eval_method/generated/methods/evalml.pipelines.PipelineBase.compute_estimator_features.html#evalml.pipelines.PipelineBase.compute_estimator_features

[codecov]

Codecov Report

Merging #1231 into main will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1231   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files         200      200           
  Lines       12468    12468           
=======================================
  Hits        12459    12459           
  Misses          9        9           

Impacted Files	Coverage Δ
...derstanding/prediction_explanations/_algorithms.py	97.14% <100.00%> (ø)
...tanding/prediction_explanations/_user_interface.py	100.00% <100.00%> (ø)
evalml/pipelines/binary_classification_pipeline.py	100.00% <100.00%> (ø)
evalml/pipelines/classification_pipeline.py	100.00% <100.00%> (ø)
evalml/pipelines/pipeline_base.py	100.00% <100.00%> (ø)
...s/prediction_explanations_tests/test_explainers.py	100.00% <100.00%> (ø)
...ation_pipeline_tests/test_binary_classification.py	100.00% <100.00%> (ø)

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[bchen1116]

LGTM

[freddyaboulton]

@angela97lin Thanks for doing this! The api ref looks great.