Test: Move extensions, settings and devPort to customizations.vscode property

[chrmarti]

Refs: devcontainers/spec#1

• anyOS @deepak1556
• anyOS @alexdima

Complexity: 2

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This requires Remote-Containers 0.233.0 or later.

• Set up a dev container. E.g., have a workspace folder with a .devcontainer.json (or .devcontainer/devcontainer.json):

{
	"image": "mcr.microsoft.com/vscode/devcontainers/base:bullseye"
}

• Verify the "extensions", "settings" and "devPort" properties still work when used as top-level properties.
• Verify they also work when used as subproperties under "customizations"."vscode".
• Verify there is IntelliSense for both variations and that there is a warning when you use a property in both locations.

Note that when adding configuration files from the built-in definitions (templates), these are still using the older top-level properties, so we have time to roll out the support first.