Update the procedure descriptions (#1181)

We have mismatches in the descriptions of the following procedures:
* `db.index.fulltext.queryNodes()`
* `db.index.fulltext.queryRelationships()`
* `db.index.vector.createNodeIndex()`

The proposed changes are taken from the code, and I suggest to modify
them a little bit. When we update the descriptions in documentation, we
have to update them in the codebase.

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Co-authored-by: Matthew Parnell <[email protected]>