docs: add snippets for Commit() with a mutator or mutations

[devbww]

This change is 

[coryan]

Thanks for doing this, maybe one of the snippets is a tad too long?

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

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google/cloud/spanner/samples/samples.cc, line 1368 at r1 (raw file):

//! [START spanner_read_write_transaction]
void ReadWriteTransaction(google::cloud::spanner::Client client) {
  //! [commit-with-mutator]

FYI, this is a fairly long snippet, did you look at the rendered Doxygen? Consider a smaller mutator, maybe like the spanner_dml_write_then_read sample?

[codecov]

Codecov Report

Merging #1374 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1374      +/-   ##
==========================================
- Coverage   94.61%   94.57%   -0.05%     
==========================================
  Files         184      184              
  Lines       15221    15228       +7     
==========================================
  Hits        14402    14402              
- Misses        819      826       +7

Impacted Files	Coverage Δ
google/cloud/spanner/samples/samples.cc	88.42% <ø> (-0.71%)	⬇️
google/cloud/spanner/client.h	100% <ø> (ø)	⬆️
google/cloud/spanner/results.h	95.83% <0%> (-4.17%)	⬇️
google/cloud/spanner/keys.h	100% <0%> (ø)	⬆️
google/cloud/spanner/internal/session.h	100% <0%> (ø)	⬆️
google/cloud/spanner/internal/transaction_impl.h	100% <0%> (ø)	⬆️
google/cloud/spanner/session_pool_options.h	100% <0%> (ø)	⬆️
google/cloud/spanner/database_admin_connection.h
...oogle/cloud/spanner/internal/instance_admin_stub.h
... and 6 more

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[devbww]

Reviewable status: complete! all files reviewed, all discussions resolved

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google/cloud/spanner/samples/samples.cc, line 1368 at r1 (raw file):

Previously, coryan (Carlos O'Ryan) wrote…

FYI, this is a fairly long snippet, did you look at the rendered Doxygen? Consider a smaller mutator, maybe like the spanner_dml_write_then_read sample?

Yes, I looked, and it didn't seem to bad. But, smaller is better.

I had tried to avoid ExecuteDml(), but I guess there is no good reason for that. So then, the spanner_dml_standard_update looks even simpler. Thanks.

[coryan]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved