* Make null member access tests as string to avoid parsing errors
* Add PSNullConditionalOperators feature to testmetadata.json
* Add Parsing tests to be skipped
* Add tabcompletion tests
This PR does 4 things:
* Adds a new cmdlet `New-PSBreakpoint` which creates new `Breakpoint` objects and writes them to the pipeline
* Adds a `-Breakpoint` parameter to `Debug-Runspace` which will receive `Breakpoint` objects
* Makes the constructors for `*Breakpoint` public for use with the API
* Makes `Debugger.GetBreakpoint(string id)` and `Debugger.GetBreakpoints()` public since `SetBreakpoints` is public
Note: `New-PSBreakpoint` and `Set-PSBreakpoint` (which already exists) are similar... but `Set-PSBreakpoint` also sets the breakpoints in the _current_ runspace. This is not ideal if we want to set breakpoints in a _different runspace than the current one_.
## PR Context
The "Attach to process" debugging experience in the PowerShell extension for VSCode is _ok_ but it's not great.
The reason it's not great is due to the `BreakAll` feature of PowerShell debugging which, when you run `Debug-Runspace`, will break at the first piece of code that gets run. This is not ideal when you "Attach to process" _and then_ run your code in the other runspace.
Today, the experience drops you in `PSReadLine`'s psm1 if PSRL is available or in the vscode PowerShell helper psm1.
It's unexpected for the user and not ideal.
This PR will allow the extension to pass in the breakpoints that need to be set initially with `BreakAll` turned off for none of this silly behavior.
### Silly behavior example
If you want a repro, try this:
PowerShell instance 1:
```
Enter-PSHostProcess -Id $otherprocesspid
Debug-Runspace 1
```
PowerShell instance 2:
```
./runfoo.ps1
```
Note that you end up NOT `runfoo.ps1`
[breaking change]
Major changes are as follows:
- Add `Enable-ExperimentalFeature` and `Disable-ExperimentalFeature` cmdlets.
- Remove `-ListAvailable` from `Get-ExperimentalFeature`.
- Add `ArgumentCompleter` for `Get-ExperimentalFeature` cmdlet.
- Refactor some existing Experimental Feature tests.
- Make `ConfigScope` public and renamed `SystemWide` to `AllUsers`. Also update experimental feature code to prefer the current user config over the all user config.
