feat: base transaction retries on error codes

[schmidt-sebastian]

Port of googleapis/nodejs-firestore#953

Implements go/transaction-retry-matrix for Java and cleans up some of the tests:

• Transaction IDs are passed as string to the helpers
• Request/response validation is centralized

[codecov]

Codecov Report

Merging #129 into master will increase coverage by 0.96%.
The diff coverage is 98.26%.

@@             Coverage Diff              @@
##             master     #129      +/-   ##
============================================
+ Coverage     71.62%   72.58%   +0.96%     
- Complexity      969      988      +19     
============================================
  Files            62       63       +1     
  Lines          5222     5270      +48     
  Branches        579      590      +11     
============================================
+ Hits           3740     3825      +85     
+ Misses         1302     1259      -43     
- Partials        180      186       +6

Impacted Files	Coverage Δ	Complexity Δ
...n/java/com/google/cloud/firestore/Transaction.java	97.5% <100%> (-0.28%)	10 <0> (-1)
.../com/google/cloud/firestore/TransactionRunner.java	100% <100%> (ø)	4 <4> (?)
...java/com/google/cloud/firestore/FirestoreImpl.java	78.62% <100%> (-3.73%)	24 <1> (ø)
...rc/main/java/com/google/cloud/firestore/Watch.java	91.55% <100%> (-0.26%)	56 <0> (-1)
...com/google/cloud/firestore/TransactionOptions.java	75% <80%> (+3.57%)	6 <3> (ø)	⬇️
...com/google/cloud/firestore/FirestoreException.java	83.33% <83.33%> (+3.33%)	9 <3> (+1)	⬆️
...rc/main/java/com/google/cloud/firestore/Query.java	90.99% <0%> (-0.74%)	100% <0%> (+6%)
...gle/cloud/firestore/v1beta1/FirestoreSettings.java	13.2% <0%> (ø)	2% <0%> (ø)	⬇️
... and 5 more

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[schmidt-sebastian]

@BenWhitehead Can you ask someone to review or review this yourself if you have time? This one is a little trickier :/

[BenWhitehead]

@schmidt-sebastian Sure, I'll dig into this tomorrow first thing.

[BenWhitehead]

Mostly looks okay. A few questions and one request to move a method.

[schmidt-sebastian]

Thank you for the review! All feedback addressed.

[BenWhitehead]

LGTM I'm looking into the Linkage Checker status check failure and will let you know if it requires anything to be change in the PR.