Merge #26164

26164: importccl: Support `IMPORT MYSQLDUMP file` r=dt a=dt

This adds a new `IMPORT` syntax:
```
IMPORT MYSQLDUMP (s3://path/to/some/file.sql) 
```
as well as variant to select a single table:
```
IMPORT TABLE simple FROM MYSQLDUMP (s3://path/to/some/file.sql) 
```

This parses the dump file to read the table schema(s), converting their the mysql-dialect `CREATE TABLE` statements to cockroach's corresponding table definitions.

When a tables named, only the named table is imported -- if the dump contains other tables, they are ignored.

The supported conversions of the various MySQL column types to corresponding Cockroach column types is somewhat documented by Cockroach `CREATE` statement in the `everything`  test case of `TestMysqldumpSchemaReader`, which is tested to correspond to the example in the `everything.sql` testdata file, though these mappings remain subject to change as we test the behaviors of the corresponding types.

This is a big step towards our mysqldump support, though we will be continuing to actively work on this for the near future, so this is a rough, initial version that we can continue to polish. Future work should allow reading create table definitions _during_ sampling, rather than prior to starting the DistSQL job, to eliminate the duplicate read cost. 

Co-authored-by: David Taylor <[email protected]>

docs/generated/sql/bnf/import_table.bnf

@@ -1,3 +1,5 @@
 import_stmt ::=
-	'IMPORT' 'TABLE' table_name 'CREATE' 'USING' string_or_placeholder import_data_format 'DATA' '(' string_or_placeholder_list ')' opt_with_options
+	'IMPORT' import_bundle_format '(' string_or_placeholder ')'
+	| 'IMPORT' 'TABLE' table_name 'FROM' import_bundle_format '(' string_or_placeholder ')'
+	| 'IMPORT' 'TABLE' table_name 'CREATE' 'USING' string_or_placeholder import_data_format 'DATA' '(' string_or_placeholder_list ')' opt_with_options
 	| 'IMPORT' 'TABLE' table_name '(' table_elem_list ')' import_data_format 'DATA' '(' string_or_placeholder_list ')' opt_with_options

docs/generated/sql/bnf/stmt_block.bnf

@@ -98,7 +98,9 @@ insert_stmt ::=
 	| opt_with_clause 'INSERT' 'INTO' insert_target insert_rest on_conflict returning_clause
 
 import_stmt ::=
-	'IMPORT' 'TABLE' table_name 'CREATE' 'USING' string_or_placeholder import_data_format 'DATA' '(' string_or_placeholder_list ')' opt_with_options
+	'IMPORT' import_bundle_format '(' string_or_placeholder ')'
+	| 'IMPORT' 'TABLE' table_name 'FROM' import_bundle_format '(' string_or_placeholder ')'
+	| 'IMPORT' 'TABLE' table_name 'CREATE' 'USING' string_or_placeholder import_data_format 'DATA' '(' string_or_placeholder_list ')' opt_with_options
 	| 'IMPORT' 'TABLE' table_name '(' table_elem_list ')' import_data_format 'DATA' '(' string_or_placeholder_list ')' opt_with_options
 
 pause_stmt ::=
@@ -327,9 +329,9 @@ explain_option_list ::=
 	( explain_option_name ) ( ( ',' explain_option_name ) )*
 
 import_data_format ::=
-	'CSV'
+	import_bundle_format
+	| 'CSV'
 	| 'MYSQLOUTFILE'
-	| 'MYSQLDUMP'
 	| 'PGCOPY'
 
 privileges ::=
@@ -355,6 +357,9 @@ on_conflict ::=
 	'ON' 'CONFLICT' opt_conf_expr 'DO' 'UPDATE' 'SET' set_clause_list where_clause
 	| 'ON' 'CONFLICT' opt_conf_expr 'DO' 'NOTHING'
 
+import_bundle_format ::=
+	'MYSQLDUMP'
+
 string_or_placeholder_list ::=
 	( string_or_placeholder ) ( ( ',' string_or_placeholder ) )*