fix: add cause to transaction errors on transaction commit

[rockwotj]

Right now if a transaction fails due to a precondition failure (which are retried, which is another bug) for example trying to update a document that doesn't exist you get a bad error message of "too many retries". Ideally retry is smarter, but this is a easy change that propagates the underlying error up to the ApiFuture result.

/cc @schmidt-sebastian @BenWhitehead

[codecov]

Codecov Report

Merging #108 into master will decrease coverage by 0.40%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #108      +/-   ##
============================================
- Coverage     71.97%   71.56%   -0.41%     
+ Complexity      997      968      -29     
============================================
  Files            62       62              
  Lines          5323     5202     -121     
  Branches        599      579      -20     
============================================
- Hits           3831     3723     -108     
+ Misses         1304     1299       -5     
+ Partials        188      180       -8     

Impacted Files	Coverage Δ	Complexity Δ
...cloud/firestore/collection/ImmutableSortedMap.java	13.95% <0.00%> (-1.96%)	1.00% <0.00%> (ø%)
...oogle/cloud/firestore/v1beta1/FirestoreClient.java	54.63% <0.00%> (-1.56%)	25.00% <0.00%> (-6.00%)
.../java/com/google/cloud/firestore/Precondition.java	68.18% <0.00%> (-1.39%)	12.00% <0.00%> (-3.00%)
...com/google/cloud/firestore/v1/FirestoreClient.java	76.28% <0.00%> (-0.86%)	31.00% <0.00%> (-6.00%)
...loud/firestore/v1beta1/stub/GrpcFirestoreStub.java	93.67% <0.00%> (-0.57%)	16.00% <0.00%> (-1.00%)
...a/com/google/cloud/firestore/FirestoreOptions.java	36.44% <0.00%> (-0.54%)	7.00% <0.00%> (ø%)
...loud/firestore/v1/stub/GrpcFirestoreAdminStub.java	94.32% <0.00%> (-0.46%)	15.00% <0.00%> (-1.00%)
...ain/java/com/google/cloud/firestore/FieldMask.java	87.09% <0.00%> (-0.41%)	13.00% <0.00%> (-2.00%)
.../firestore/v1beta1/stub/FirestoreStubSettings.java	79.26% <0.00%> (-0.38%)	22.00% <0.00%> (-1.00%)
...gle/cloud/firestore/v1/stub/GrpcFirestoreStub.java	96.04% <0.00%> (-0.36%)	19.00% <0.00%> (-1.00%)
... and 9 more

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[BenWhitehead]

@rockwotj Can you run mvn com.coveo:fmt-maven-plugin:format to get the code format pre-submit to pass?

[BenWhitehead]

Change looks good, just need to run the formatter.

[schmidt-sebastian]

FYI: We will shortly be addressing the transaction retry behavior across all of our SDKs.

[schmidt-sebastian]

@rockwotj Can you update the PR title to follow conventionalcommits.org?

It this case it would be: "fix: ddd cause to transaction errors on transaction commit"

[BenWhitehead]

Thanks for the improvement @rockwotj!