Exposing a DisableVariableSubstitution on the Parser object

[Matteo-T]

Addressing issues #1936 and #1937.

With this change, I'm adding a new property on the Parser object DisableVariableSubstitution to allow the parsing to completely ignore elements in the T-SQL fragment that may look like Variables, thus allowing consumers of the Parser (e.g. SQL Server Powershell Invoke-Sqlcmd cmdlet) to micking the behavior of sqlcmd.exe -x which completely ignores such variables during parsing.

This property has a default value of false (for backward compatibility).

This PR also introduced the fix for #1937 is just to allow the Parser to be a little more forgiving and avoid throwing a NRE when the caller is not passing in any IVariableResolver, which most likely means "I do not need/care for any variable substitution, so don't bother".

While combining the 2 fixes, it made sense to change the default value for DisableVariableSubstitution to be true when the IVariableResolver is null (this is safe, since no existing code out there allowed it before... so no existing consumer should be surprised by this change).

This PR does not mean to address #1938, although it is somehow related to it.

[Matteo-T]

@cheenamalhotra - could you advise on a couple of things? Like, is there a way to link the PR to the issues? Also, are there other things that need to happen before this PR can go in? Like updating labels, milestons, projects, etc? I suppose that whoever is triaging the issues is going to do that? I need to be educated... Thanks!

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In reply to: 1465862486

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In reply to: 1465862486

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In reply to: 1465862486

[Charles-Gagnon]

For linking items to a PR the easiest way is to use one of the closing keywords : https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword

Note that you have to put it in front of each issue to close - e.g.

Fixes https://github.com/microsoft/sqltoolsservice/issues/1936
Fixes https://github.com/microsoft/sqltoolsservice/issues/1937

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In reply to: 1466382921

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In reply to: 1466382921

[Matteo-T]

I went with the UI (Development): it resembles ADO after all...

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In reply to: 1466382921