Microsoft.CodeAnalysis.Semantics renamed to Microsoft.CodeAnalysis.Operations

1. Rename -Expression and -Statement nodes to -Operation
2. Ensure all IOperation interfaces are suffixed with Operation
3. Rename all OperationKinds to match the corresponding IOperation interfaces without the prefix I and suffix Operation. Also fixed the operation ranges to be all contigous range.
4. Rename all the OperationVisitor methods to also match the corresponding IOperation interfaces without the prefix I and suffix Operation.
5. Merge the following interfaces which were semantically same, but syntactically different:
   1. IInvalidExpression and IInvalidStatement merged to IInvalidOperation
   2. IIfStatement and IConditionalExpression merged to IConditionalOperation
6. Update doc comments for all IOperation APIs to have 2 sections:
   1. Summary section which cites pure semantics of the API without any mention of the language, expression/statement, current usage/implementation, etc.
   2. Current usage para which cites how these APIs are used in current C# and VB implementation of these interfaces.

Addresses Preview and Documentation items from #22719

this is easy step. just spliting all IOperations as its own files and put them in its own folder