Add an interpreter base for function creation

[Hydrocharged]

This adds the base of an interpreter, upon which CREATE FUNCTION and CREATE PROCEDURE will convert their contents to. Only the interpreter portion is partially implemented, along with a temporary example function and accompanying test to ensure that it works.

The next major step is to add parsing support for all of the statements that we'll need, as they do not yet exist (hence why the temporary example function's operations were manually created, although the conversion should result in the same output). The last major step will be to convert from the PL/pgSQL code to the operations that our interpreter expects.

The original intention was to implement as much of this in GMS as possible, however for now, the bulk of it will exist in Doltgres as I couldn't quite reconcile the proper way to implement it there without diving more fully into MySQL's CREATE FUNCTION and CREATE PROCEDURE support (rather than simply relying on memory). This is something that I'll revisit in a later PR, as I feel it'll be easier to do once I have a relatively complete implementation done in Doltgres.

Related PR:

• Added the concept of an interpreter expression go-mysql-server#2835

[github-actions]

	Main	PR
covering_index_scan_postgres	351.49/s	360.50/s	+2.5%
index_join_postgres	153.95/s	154.08/s	0.0%
index_join_scan_postgres	183.54/s	184.39/s	+0.4%
index_scan_postgres	12.70/s	12.63/s	-0.6%
oltp_point_select	2792.98/s	2796.80/s	+0.1%
oltp_read_only	1878.47/s	1886.05/s	+0.4%
select_random_points	112.34/s	113.69/s	+1.2%
select_random_ranges	127.71/s	126.48/s	-1.0%
table_scan_postgres	11.88/s	11.98/s	+0.8%
types_table_scan_postgres	5.67/s	5.65/s	-0.4%

[github-actions]

	Main	PR
Total	42090	42090
Successful	15537	15537
Failures	26553	26553
Partial Successes1	5226	5226

	Main	PR
Successful	36.9138%	36.9138%
Failures	63.0862%	63.0862%

Footnotes

1. These are tests that we're marking as Successful, however they do not match the expected output in some way. This is due to small differences, such as different wording on the error messages, or the column names being incorrect while the data itself is correct. ↩

[zachmu]

Overall seems pretty reasonable, a good start.

Main comment is that skipping backwards iteratively seems like an unnecessary complication, it should be possible to keep track of statements and jump to them directly.