BigQuery: Fix timestamp parsing regression

[pmakani]

Fixes#4500

[codecov]

Codecov Report

Merging #4510 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@ Coverage Diff @@## master #4510 +/- ##
============================================
- Coverage 49.16% 49.14% -0.02% + Complexity 21929 21927 -2 
============================================
Files 2077 2078 +1 Lines 207074 207184 +110 Branches 24097 24106 +9 ============================================
+ Hits 101801 101815 +14 - Misses 97100 97196 +96 
Partials 8173 8173

Impacted Files	Coverage Δ	Complexity Δ
...com/google/cloud/bigquery/QueryParameterValue.java	68.84% <100%> (+3.51%)	43 <1> (ø)	⬇️
...loud/bigtable/data/v2/internal/RequestContext.java	33.33% <0%> (-66.67%)	2% <0%> (ø)
.../bigtable/admin/v2/BigtableTableAdminSettings.java	78.37% <0%> (-21.63%)	6% <0%> (ø)
...gtable/admin/v2/BigtableInstanceAdminSettings.java	82.14% <0%> (-17.86%)	5% <0%> (ø)
...ble/data/v2/stub/EnhancedBigtableStubSettings.java	93.19% <0%> (-5.37%)	15% <0%> (-2%)
...gle/cloud/bigtable/data/v2/BigtableDataClient.java	84.31% <0%> (-5.27%)	32% <0%> (ø)
...e/cloud/bigtable/data/v2/BigtableDataSettings.java	31.7% <0%> (-3.43%)	3% <0%> (ø)
...le/cloud/bigtable/data/v2/models/InstanceName.java	0% <0%> (ø)	0% <0%> (?)

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[sduskis]

Can we replace timestampFormatter with your configuration for timestampValidator?

[pmakani]

It can't be done with single formatter.