`Read-Host` calls into `$Host.UI.Prompt()`. However, this method is also used when the host prompts for mandatory parameters that aren't provided. The method expects to be called when given a `FieldDescription` and if the input starts with `!` it enters `CommandPromptMode`. In this mode, you can type `!?` to request help, for example. However this mode is not something you can use via `Read-Host` (only if calling `$Host.UI.Prompt()` directly passing in a well constructed `FieldDescription`). When using `Read-Host -Prompt`, the cmdlet creates a `FieldDescription` where the name is the prompt and the rest of the properties are empty.
The fix is that if `Label` is empty, we can assume it's being called from `Read-Host` rather than being called to prompt for a mandatory parameter and thus not enter `CommandPromptMode`.
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`
Steve Lee