"Variables" column tightly coupled to the VARIABLES view

**Description**
Memory Inspector editors allow enabling a Variables column. A nice and useful feature but its enablement is completely unintuitive and undocumented. In other words, the column is eventually populated _only_ if the VARIABLES view is visible and its nodes are expanded. Current implementation seems to intercept debug adapter message/responses that are related to variables retrieval and only populate the Variables column when such messages are intercepted.

From my experiments, I have never been able to see anything in the Variables column when using CPPDBG debug adapter. Whereas when using Cortex Debug, the behavior is as described above.

Requests:
1. Document the dependency of the Variables column from Memory Inspector editors. Make it clear that Variables column depends on the visibility/expanded state of the nodes from VARIABLES view.
2. When Variables column is enabled, make sure the Memory Inspector initiates requests for locals/globals/statics instead of relying on other entities (e.g. VARIABLES view) to make such requests and then simply track/intercept DAP messages.

**Additional information**

Memory Inspector editor with VARIABLES collapsed:


Memory Inspector editor with VARIABLES nodes expanded: