improve support for T-SQL EXECUTE statements

[lovasoa]

This adds the following features from the Microsoft SQL Server EXECUTE statement:

Support EXEC as an alias to EXECUTE
fixes #1275

Support schema qualified stored procedures
fixes #1276

support unnamed parameters in mssql EXECUTE stored procedure calls
fixes #1489

@alamb, I would love if we could get this merge, since this is blocking for sqlpage/SQLPage#655

[lovasoa]

@alamb , what do you think? Can we merge this like that?

[alamb]

I re-reviewed this PR -- and it looks good to me. Thank you @lovasoa

I agree with the generic thoughts from @iffyio about has_parenthesis and testing across all dialects, but I also agree there is no reason to gate merging this PR on those improvements

Thank you both as always

[coveralls]

Pull Request Test Coverage Report for Build 11631184629

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 39 of 44 (88.64%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.004%) to 89.375%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/mod.rs	6	8	75.0%
tests/sqlparser_common.rs	19	22	86.36%

Totals
Change from base Build 11580333290:	-0.004%
Covered Lines:	30442
Relevant Lines:	34061

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💛 - Coveralls

[lovasoa]

Great, thank you @alamb and @iffyio ! The next version of SQLPage is going to be great with all these sqlparser improvements !