[mssql/oracle] Support CROSS/OUTER APPLY

[nickolay]

From the commit message:

T-SQL (and Oracle) support non-standard syntax, which is similar in
functionality to LATERAL joins in ANSI and PostgreSQL
https://blog.jooq.org/tag/lateral-derived-table/: it allows to use
the columns from the tables defined to the left of APPLY in the
"derived tables" (subqueries) to the right of APPLY. Unlike ANSI
LATERAL (but like Postgres' implementation), APPLY is also used with
table-valued function calls.

Despite them being similar, we represent "APPLY" joins with
JoinOperators of its own (CrossApply and OuterApply). Doing
otherwise seemed like it would cause unnecessary confusion, as those
interested in dialect-specific parsing would probably not expect APPLY
being parsed as LATERAL, and those wanting to forbid non-standard SQL
would not be helped by this either.

This also renames existing JoinOperator::Cross -> CrossJoin to avoid
confusion with CrossApply.

This also includes a fix for the bad merge in #118.

[coveralls]

Pull Request Test Coverage Report for Build 361

• 24 of 24 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
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[coveralls]

Pull Request Test Coverage Report for Build 361

• 24 of 24 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at ?%

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Totals
Change from base Build 358:	0.0%
Covered Lines:
Relevant Lines:	0

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💛 - Coveralls

[benesch]

LGTM!

[benesch]

(And thanks for explicitly clarifying in your commit message why you chose not to unify lateral and apply—that was super helpful!)