Provide diagnostic marker API in $psEditor

It would be useful if there was an API to add diagnostic markers to script files so that any editor command could add "squigglies" to arbitrary regions of an open file. Markers would be added in relation to a named "layer" which would allow Editor Services to keep track of a unique set of markers for each module or use case.

The API might look something like this:

$file = $context.CurrentFile
# OR: $file = $psEditor.Workspace.GetFile("filePath.ext")
$file.SetMarkers("MarkerLayerName", markerArray)

We should also provide an API for clearing markers, either for a specific layer or for all layers:

$file.ClearMarkers("MarkerLayerName")
$file.ClearMarkers()

Once this API exists, I'll use it to implement the new integration model for PSScriptAnalyzer in issue #213.

FEEDBACK NEEDED: Is SetMarkers good enough or should it be SetFileMarkers, SetDiagnosticMarkers or something else?

まず、既存の $psEditor ファイル API と issue #213 を確認し、診断マーカーがどのように利用されるかを理解します。マーカーレイヤーと命名の設計を確定し、その後、任意のファイル領域と各レイヤーに対する SetMarkers および ClearMarkers の動作を定義します。