BigQuery: Add routines support

[shollyman]

This adds java support for bigquery routines, which enables API access to a persistent functions and (soon) stored procedures. Routines exist inside of BigQuery datasets, just like tables and BQML models.

UDF documentation:
https://cloud.google.com/bigquery/docs/reference/standard-sql/user-defined-functions
Routines REST documentation:
https://cloud.google.com/bigquery/docs/reference/rest/v2/routines

This PR adds:
CRUD operations for manipulating Routine resources. It models the same structure used for Tables and Models. There's a RoutineId class for the qualified reference, a RoutineInfo for metadata and a Routine class for binding to the service operations like create/update/delete. Submessages like arguments (RoutineArgument) are also implemented as classes.

StandardSQLDataType,StandardSQLField,StandardSQLStructType veneers for communicating type information using standard sql typing. These are used for communicating datatype information for inputs/outputs in routines.

Augments query stats: In addition to using the API directly, you can also manipulate routines using the query language (e.g. CREATE FUNCTION ... AS ...). Statistics provided as part of the query job include the statement type, and when using appropriate DDL queries the DDL target routine.

There's some other cleanup around typos/docs, as well as filling in missing things like statements in the StatementType enum.

[shollyman]

Failure is due to unrelated flaky test in BQ, sent #5592 to address.

[codecov]

Codecov Report

Merging #5591 into master will increase coverage by 0.37%.
The diff coverage is 53.65%.

@@ Coverage Diff @@## master #5591 +/- ##
============================================
+ Coverage 46.71% 47.09% +0.37% - Complexity 24647 25078 +431 
============================================
Files 2351 2389 +38 Lines 256185 259732 +3547 Branches 29333 29397 +64 ============================================
+ Hits 119688 122317 +2629 - Misses 127575 128454 +879 - Partials 8922 8961 +39

Impacted Files	Coverage Δ	Complexity Δ
.../com/google/cloud/bigquery/spi/v2/BigQueryRpc.java	77.77% <ø> (ø)	0 <0> (ø)	⬇️
...e/cloud/bigquery/testing/RemoteBigQueryHelper.java	61.4% <0%> (-1.1%)	6 <0> (ø)
...n/java/com/google/cloud/bigquery/BigQueryImpl.java	66.78% <0%> (-13.22%)	57 <0> (ø)
.../google/cloud/bigquery/spi/v2/HttpBigQueryRpc.java	5.3% <0%> (-0.8%)	2 <0> (ø)
.../java/com/google/cloud/bigquery/JobStatistics.java	93.91% <100%> (+0.34%)	13 <0> (ø)	⬇️
...in/java/com/google/cloud/bigquery/RoutineInfo.java	66.95% <66.95%> (ø)	20 <20> (?)
...com/google/cloud/bigquery/StandardSQLDataType.java	75% <75%> (ø)	7 <7> (?)
...main/java/com/google/cloud/bigquery/RoutineId.java	76.92% <76.92%> (ø)	13 <13> (?)
.../main/java/com/google/cloud/bigquery/BigQuery.java	78.75% <80.76%> (+0.31%)	0 <0> (ø)	⬇️
...c/main/java/com/google/cloud/bigquery/Routine.java	82.35% <82.35%> (ø)	11 <11> (?)
... and 46 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d67dc01...d9a549d. Read the comment docs.

[sduskis]

Should this be package private? (Same with other public methods in package private classes)

[shollyman]

It's probably reasonable, we extend Option but don't appear to extend each of the various typed options beyond that. Filed https://github.com/googleapis/google-cloud-java/issues/5728 to followup on visibility more generally.