Support snowflake alter table swap with

[pawel-big-lebowski]

Support snowflake's alter table swap with syntax. See doc.

ALTER TABLE tab1 SWAP WITH tab2

[alamb]

Thank you @pawel-big-lebowski

[coveralls]

Pull Request Test Coverage Report for Build 4351457868

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 285 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.004%) to 86.122%

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Files with Coverage Reduction	New Missed Lines	%
src/ast/ddl.rs	32	82.16%
src/parser.rs	253	83.01%

Totals
Change from base Build 4345926686:	0.004%
Covered Lines:	13485
Relevant Lines:	15658

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💛 - Coveralls

[alamb]

@pawel-big-lebowski you please fix the CI errors on this PR?

[pawel-big-lebowski]

@alamb Sure.

[alamb]

Thank you for the contribution @pawel-big-lebowski