BigQuery: update signature for ML model access to label/feature columns.

[shollyman]

This is a breaking change to a @BetaApi within BigQuery.

It swaps in a new veneer StandardSQLField type in place of the underlying
discovery type for getting information about the feature and label columns
from ML models, which was functionality introduced in:
#5214

[codecov]

Codecov Report

Merging #5732 into master will decrease coverage by 0.38%.
The diff coverage is 81.81%.

@@ Coverage Diff @@## master #5732 +/- ##
============================================
- Coverage 47.09% 46.71% -0.39% + Complexity 25063 23629 -1434 
============================================
Files 2389 2389 Lines 259743 254614 -5129 Branches 29404 29257 -147 ============================================
- Hits 122320 118934 -3386 + Misses 128462 127626 -836 + Partials 8961 8054 -907

Impacted Files	Coverage Δ	Complexity Δ
...src/main/java/com/google/cloud/bigquery/Model.java	67.27% <ø> (ø)	12 <0> (ø)	⬇️
...main/java/com/google/cloud/bigquery/ModelInfo.java	75.53% <81.81%> (-0.58%)	21 <0> (ø)
...m/google/cloud/vision/v1/ImageAnnotatorClient.java	58.69% <0%> (-3.31%)	15% <0%> (-4%)
...e/cloud/vision/v1p4beta1/ImageAnnotatorClient.java	58.69% <0%> (-3.31%)	15% <0%> (-4%)
...e/cloud/vision/v1p3beta1/ImageAnnotatorClient.java	47.05% <0%> (-2.95%)	9% <0%> (-2%)
...e/cloud/vision/v1p2beta1/ImageAnnotatorClient.java	47.05% <0%> (-2.95%)	9% <0%> (-2%)
.../java/com/google/cloud/speech/v1/SpeechClient.java	48.57% <0%> (-2.78%)	10% <0%> (-2%)
...om/google/cloud/speech/v1p1beta1/SpeechClient.java	48.57% <0%> (-2.78%)	10% <0%> (-2%)
...d/webrisk/v1beta1/WebRiskServiceV1Beta1Client.java	63.41% <0%> (-2.5%)	12% <0%> (-3%)
...ogle/cloud/texttospeech/v1/TextToSpeechClient.java	55.88% <0%> (-2.46%)	9% <0%> (-2%)
... and 624 more

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[tswast]

LGTM. No tests to update? I guess I didn't really check for all properties on the Models API stats, either.

[shollyman]

LGTM. No tests to update? I guess I didn't really check for all properties on the Models API stats, either.

The tests accessed the data transitively without declaring the intermediate types. The types changed but the getter names didn't. Ex:

 assertEquals(model.getFeatureColumns().get(0).getName(), "f1");
assertEquals(model.getLabelColumns().get(0).getName(), "predicted_label");

[kolea2]

Where is this annotated with @BetaApi? Just want to make sure we don't introduce a breaking change to something that wasn't labeled as such.

[shollyman]

The feature represents readonly properties provided by the BQ backend, so I marked it as BetaApi on the public getters in ModelInfo. The internal builder was not annotated this way.

[kolea2]

Ah, sorry didn't realize this wasn't a public method. SGTM.

comment addressed