Allow Bigtable Query to be copied

[rculbertson]

Added a new create method to the Bigtable Query object that behaves like a
copy constructor. It takes an existing Query object and performs a deep copy.

This is to address #5550, but this could be useful in other situations as well.

[codecov]

Codecov Report

Merging #5551 into master will decrease coverage by 0.31%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #5551      +/-   ##
============================================
- Coverage     50.85%   50.54%   -0.32%     
+ Complexity    24192    22791    -1401     
============================================
  Files          2270     2270              
  Lines        230115   225273    -4842     
  Branches      25009    24896     -113     
============================================
- Hits         117035   113859    -3176     
+ Misses       104442   103670     -772     
+ Partials       8638     7744     -894

Impacted Files	Coverage Δ	Complexity Δ
...om/google/cloud/bigtable/data/v2/models/Query.java	66.66% <100%> (+0.34%)	23 <3> (+1)	⬆️
...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%)
...cloud/texttospeech/v1beta1/TextToSpeechClient.java	55.88% <0%> (-2.46%)	9% <0%> (-2%)
... and 537 more

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[sduskis]

As per this comment (#5550 (comment)), I'm going to close this PR. @igorbernstein2 and crew will work on another approach.