Clear secondary streams on primary PowerShell object

Currently we reuse the same PowerShell object for every script invocation/prompt evaluation, but we aren't clearing the streams afterward. Example:

PS> $context = $psEditor.Components.Get([Microsoft.PowerShell.EditorServices.PowerShellContext])
PS> $ps = $context.GetType().GetField('powerShell', 60).GetValue($context)
PS> $ps.Streams.Information
# <Empty>
PS> Write-Host 'first message'
PS> $ps.Streams.Information
# first message
PS> Write-Host 'second message'
PS> $ps.Streams.Information
# first message
# second message

Same for the other streams e.g. warning, verbose, debug, and progress (even though progress is not shown, the record is still stored until the end of the session)

Depending on how long the PSIC is left open and how much these streams are being written to, this could be the cause of some reported memory usage issues.

从复用主 PowerShell 对象来执行脚本调用和提示评估的代码开始，然后检查其 Streams.Information、warning、verbose、debug 和 progress 集合。复现 issue 中显示的累积情况，并跟踪每次调用何时完成。完成的标准是，次级流记录不会在调用之间持续存在，包括 progress 记录；如果存在相关测试，则该行为也应由这些测试覆盖。