[breaking] Deprecate the MOI.Test submodule (#1407)

* [breaking] Deprecate the MOI.Test submodule by moving it to MOI.DeprecatedTests

This is the first step in a series of pull requests to rewrite our
existing testing infrastructure. Rather than rewriting it in-place,
we're starting afresh to simplify the transition process for solvers.

* Fix segfault

Author: odow

docs/src/manual/implementing.md

@@ -1,4 +1,4 @@
-module Test
+module DeprecatedTest
 
 using MathOptInterface
 const MOI = MathOptInterface

docs/src/submodules/Test/overview.md

@@ -540,7 +540,7 @@ function solve_start_soc(model::MOI.ModelLike, config::Config{T}) where {T}
     end
     if config.solve
         MOI.optimize!(model)
-        MOI.Test.test_model_solution(
+        test_model_solution(
             model,
             config;
             objective_value = o,