feat: add support for user defined TVFs

[stephaniewang526]

Allow BigQuery client library users to define table-valued functions (TVFs) that return table data.

[codecov]

Codecov Report

Merging #1278 (e9fc698) into master (f006fa9) will decrease coverage by 0.07%.
The diff coverage is 61.53%.

❗ Current head e9fc698 differs from pull request most recent head 6aac2ed. Consider uploading reports for the commit 6aac2ed to get more accurate results

@@ Coverage Diff @@ ## master #1278 +/- ## ============================================ - Coverage 80.19% 80.12% -0.08%  - Complexity 1271 1277 +6  ============================================ Files 79 80 +1 Lines 6639 6665 +26 Branches 767 771 +4 ============================================ + Hits 5324 5340 +16  - Misses 917 923 +6  - Partials 398 402 +4 

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/com/google/cloud/bigquery/Routine.java	78.94% <0.00%> (-2.88%)	12.00 <0.00> (ø)
...in/java/com/google/cloud/bigquery/RoutineInfo.java	88.81% <40.00%> (-3.68%)	26.00 <1.00> (+1.00)	⬇️
...om/google/cloud/bigquery/StandardSQLTableType.java	85.71% <85.71%> (ø)	5.00 <5.00> (?)

---

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 f006fa9...6aac2ed. Read the comment docs.

[shollyman]

Looks good, but seems like you should augment google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/RoutineTest.java to exercise the optional returnTableType so you retain coverage.

[stephaniewang526]

Looks good, but seems like you should augment google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/RoutineTest.java to exercise the optional returnTableType so you retain coverage.

added additional test in RoutineTest