go: fix ignored page token bug in iterator

[noahdietz]

A mirror of the fix submitted in gapic-generator-go#128, the PageToken was not being respected at iterator creation. It was being ignored entirely if supplied when creating a new iterator.

added @jadekler for approval of changes to generated output. This is technically a bug in all Go GAPICs today. We will need to regen once the change is released.

[codecov]

Codecov Report

Merging #2716 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2716   +/-   ##
=========================================
  Coverage     86.95%   86.95%           
  Complexity     5622     5622           
=========================================
  Files           468      468           
  Lines         22446    22446           
  Branches       2433     2433           
=========================================
  Hits          19519    19519           
  Misses         2079     2079           
  Partials        848      848

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[codecov]

Codecov Report

Merging #2716 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2716   +/-   ##
=========================================
  Coverage     86.95%   86.95%           
  Complexity     5622     5622           
=========================================
  Files           468      468           
  Lines         22446    22446           
  Branches       2433     2433           
=========================================
  Hits          19519    19519           
  Misses         2079     2079           
  Partials        848      848

---

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[codecov]

Codecov Report

Merging #2716 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2716   +/-   ##
=========================================
  Coverage     86.95%   86.95%           
  Complexity     5622     5622           
=========================================
  Files           468      468           
  Lines         22446    22446           
  Branches       2433     2433           
=========================================
  Hits          19519    19519           
  Misses         2079     2079           
  Partials        848      848

---

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Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

Merging #2716 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2716   +/-   ##
=========================================
  Coverage     86.95%   86.95%           
  Complexity     5622     5622           
=========================================
  Files           468      468           
  Lines         22446    22446           
  Branches       2433     2433           
=========================================
  Hits          19519    19519           
  Misses         2079     2079           
  Partials        848      848

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[pongad]

I'll let @jadekler sign off, but this LGTM.