Test slow variables and call stack improvements

[weinand]

Test for #5645:

• Windows | OS X | Linux - @isidorn

For improving the stepping experience for programs with lots of local variables, we've made the following adjustments:

• if a scope has more than 100 local variables, VS Code no longer auto expands that scope
• after the user has expanded the scope only the first 100 local variables are shown.
• in both cases the name of the scope reflects the fact that there many locals and only a subset is shown.

Verify that the following use case from the TypeScript transpiler works smoother:

1. git clone https://github.com/Microsoft/TypeScript.git
2. npm install, npm install jake
3. jake local
4. set breakpoint in checker.ts:47
5. Use the following launch.json. Please notice that you replace <<>> with a valid path.
6. Launch and single step through checker.ts.

Verify that stepping is reasonable fast.

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Launch",
            "type": "node",
            "request": "launch",
            "program": "${workspaceRoot}/src/compiler/tsc.ts",
            "args": ["<<<PATH TO ANY TS FILE>>>"],
            "cwd": "${workspaceRoot}",
            "runtimeArgs": [
                "--nolazy"
            ],
            "sourceMaps": true,
            "outDir": "${workspaceRoot}/built/local"
        }
    ]
}

If this works for you please add the VERIFIED label to #5645.