deprecate the top-level activeParameter property or update the documentation to clearly explain why there are two of them

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if i'm understanding the situation correctly (after skimming through microsoft/vscode#94637), it seems that SignatureInformation.activeParameter is supposed to replace the top-level one in textDocument/signatureHelp. but currently there are two of them and the documentation doesn't really explain why. in fact the documentation on the top level one seems to imply the opposite, since it says the following:

In future version of the protocol this property might become mandatory to better express the active parameter if the active signature does have any.

i think either the top-level one should be explicitly marked as deprecated, or the documentation should be updated to clarify which one is preferred.