GValue parity across all GLVs and parameterized feature tests

CHANGELOG.asciidoc

@@ -58,6 +58,8 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 * Modified HTTP API to expect gremlin-lang strings for parameters and update all GLVs to send requests in new format.
 * Added string parameter parsing to `GremlinServer` to prevent traversal injection and excessive nesting depths.
 * Modified all GLVs to detect unsupported types in `GremlinLang` and throw consistent error for that case.
+* Extended `GValue` parameterization to all GLVs (`gremlin-python`, `gremlin-go`, `gremlin-javascript`, `gremlin-dotnet`), allowing parameters to be passed directly in traversals as in Java.
+* Relaxed `GValue` name validation by removing the reserved leading underscore restriction.
 * Added GraphBinary 4.0 `Graph` (`0x10`) serializer/deserializer to `gremlin-javascript`, `gremlin-dotnet`, and `gremlin-go` so that `subgraph()` results are returned as a detached `Graph` data container.
 
 [[release-4-0-0-beta-2]]

docs/src/reference/gremlin-variants.asciidoc

@@ -337,7 +337,8 @@ the traversal to utilize a parameter in place of a literal.
 
 [source,go]
 ----
-g.V().Has("name", gremlingo.NewGValue("name", "marko"))
+g.V().Has("name", gremlingo.GValue{Name: "name", Value: "marko"})
+g.MergeV(gremlingo.GValue{Name: "vertexPattern", Value: map[interface{}]interface{}{"name": "marko"}})
 ----
 
 [[gremlin-go-scripts]]
@@ -1852,8 +1853,17 @@ Promise.all([
 [[gremlin-javascript-gvalue]]
 === GValue Parameterization
 
-IMPORTANT: 4.0.0-beta.2 Release - `GValue` parameterization is not yet implemented for the JavaScript driver. This
-functionality is planned for a future release.
+A `GValue` is an encapsulation of a parameter name and value. A <<traversal-parameterization,subset of gremlin steps>>
+are able to accept GValues. When constructing a `GraphTraversal` with such steps in JavaScript, a GValue may be passed
+in the traversal to utilize a parameter in place of a literal.
+
+[source,javascript]
+----
+const GValue = gremlin.process.GValue;
+
+g.V().has('name', new GValue('name', 'marko'));
+g.mergeV(new GValue('vertexPattern', { name: 'marko' }));
+----
 
 [[gremlin-javascript-scripts]]
 === Submitting Scripts
@@ -2398,6 +2408,8 @@ the traversal to utilize a parameter in place of a literal.
 [source,csharp]
 ----
 g.V().Has("name", new GValue<string>("name", "marko"));
+g.MergeV(new GValue<IDictionary<object, object>>("vertexPattern",
+    new Dictionary<object, object> { { "name", "marko" } }));
 ----
 
 [[gremlin-dotnet-scripts]]

docs/src/upgrade/release-4.x.x.asciidoc

@@ -471,6 +471,22 @@ beyond this limit will be rejected with an error.
 
 See: link:https://issues.apache.org/jira/browse/TINKERPOP-3247[TINKERPOP-3247]
 
+==== GValue in the Language Variants
+
+`GValue`, the named query-parameter wrapper introduced for Java in 3.8.0, is now available as a client-side API in all
+of the Gremlin Language Variants. Users of the Python, JavaScript, .NET, and Go drivers can construct a `GValue` and
+pass it to a parameterizable step; the driver sends the value to the server as a named parameter rather than inlining
+it as a literal. See the "GValue Parameterization" reference documentation for
+link:https://tinkerpop.apache.org/docs/4.0.0/reference/#gremlin-java-gvalue[Java],
+link:https://tinkerpop.apache.org/docs/4.0.0/reference/#gremlin-python-gvalue[Python],
+link:https://tinkerpop.apache.org/docs/4.0.0/reference/#gremlin-javascript-gvalue[JavaScript],
+link:https://tinkerpop.apache.org/docs/4.0.0/reference/#gremlin-dotnet-gvalue[.NET], and
+link:https://tinkerpop.apache.org/docs/4.0.0/reference/#gremlin-go-gvalue[Go] for construction syntax and examples.
+
+The leading-underscore restriction on `GValue` names that was present in 3.8.0 has been removed. Parameter names
+beginning with `_` are now accepted in Java and across all language variants. The only remaining constraints are that
+a `GValue` may not wrap another `GValue`, and (in the non-Java drivers) its name may not be null.
+
 ==== JavaScript Typed Numeric Wrappers
 
 JavaScript has a single `Number` type (IEEE 754 double) which loses the distinction between Gremlin numeric types like