Merged PRs

dolt

1973: Fixed behavior for CONVERT(x USING y)
The CONVERT(x USING y) expression allows us to convert between character sets. When a string does not have a representing rune in the target character set, it should be replaced by a question mark. This is consistent with MySQL. Our previous behavior logged an error, which is valid in many scenarios, but not for this particular expression.
1970: sql: ExternalStoredProcedureDetails: Add the ability to mark stored procedures read-only.
1969: Added a QueryEngine abstraction to engine tests to allow us to run engine tests on a running server
Implementation is partially working. Lots of errors when used in tests, some of which are real and some of which are issues with test definitions. Will keep working on this over time, but want to get the necessary refactoring in before continuing.

Read Tests	MySQL	Dolt	Multiple
covering_index_scan	2.11	2.97	1.4
groupby_scan	12.98	17.95	1.4
index_join	1.27	4.74	3.7
index_join_scan	1.21	2.26	1.9
index_scan	32.53	58.92	1.8
oltp_point_select	0.14	0.41	2.9
oltp_read_only	2.71	7.43	2.7
select_random_points	0.31	0.73	2.4
select_random_ranges	0.37	1.04	2.8
table_scan	32.53	57.87	1.8
types_table_scan	75.82	167.44	2.2
reads_mean_multiplier			2.3

Write Tests	MySQL	Dolt	Multiple
bulk_insert	0.001	0.001	1.0
oltp_delete_insert	4.74	5.67	1.2
oltp_insert	2.3	2.76	1.2
oltp_read_write	5.99	14.46	2.4
oltp_update_index	2.35	2.81	1.2
oltp_update_non_index	2.61	2.81	1.1
oltp_write_only	3.43	7.17	2.1
types_delete_insert	4.49	5.88	1.3
writes_mean_multiplier			1.4

Overall Mean Multiple	1.9