Support BoundUsingLocalDeclarations in IOperation and CFG

[chsienki]

BoundUsingLocalDeclarations are currently implemented as OperationKind.None, and return the List of local declarations as its children. We should implement this correctly with an Operation node.

We should also support CFG correctly with using declarations. Currently we report the using declaration as OperationKind.None in a single block, and thus don't report the actual underlying block structure generated by lowering.

[jcouv update:] When fixing this, let's also verify IDE behavior got fixed. For example #36502

[jcouv]

Once fixed, please verify this scenario (copied from #33464):

Using-declaration should not trigger RemoveUnusedValues.

I suspect this is a compiler issue, as the AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer relies on the control flow graph to determine how variables are used.

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We should also test ExtractMethod on a using-declaration (tracked by this issue)

[yyjdelete]

Maybe the same as #33464.
An quick fix Inline temporary variable should not be provided for the first x1.

using var x1 = File.OpenText("test");
var x2 = x1.ReadToEnd();

Expect: Inline temporary variable should not be provided.
Actual:

var x2 = File.OpenText("test").ReadToEnd();

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[jcouv update:] Yes. Also we can close this issue when we've fixed/verified the InlineVariable scenario.

[mavasani]

#36502 - another report where IOperation/CFG based analyses in IDE is falling over due to this issue. There are now at least 4 known IDE features that give false results due to this missing support.