Adding Execution Plan Editor to ADS (#18696)

* Pushing Execution Plan Editor

* Renaming class
Handling error

* Awaiting for handlers to be registered

* Addressing some PR comments

* Fixing return type for provider

* Fixing editor id and removing unnecessary overrides

* Adding a namespace

* adding execution plan namespace

* Adding protocol comment

* Fixing if logic

* Fixing error message

* Cleaning up code

* cleanup code

* Adding help comments

* Fixing method call

* Using path.ts to get the base file name

* converting to lambda functions

* Adding comment for run action

* Fixing pr comments

* Fixing editor label

* Fixing doc comments

* Adding some more comments

* Fixign branding in comments

extensions/mssql/package.json

@@ -514,14 +514,14 @@
         {
           "command": "mssql.designTable",
           "when": "connectionProvider == MSSQL && nodeType == Table && config.workbench.enablePreviewFeatures",
-          "group":"connection@3"
+          "group": "connection@3"
         },
         {
           "command": "mssql.newTable",
           "when": "connectionProvider == MSSQL && nodeType == Folder && nodeLabel == Tables && config.workbench.enablePreviewFeatures",
-          "group":"connection@1"
+          "group": "connection@1"
         }
-			],
+      ],
       "notebook/toolbar": [
         {
           "command": "mssql.exportNotebookToSql",
@@ -759,6 +759,9 @@
     "connectionProvider": {
       "providerId": "MSSQL",
       "displayName": "%mssql.provider.displayName%",
+      "supportedExecutionPlanFileExtensions": [
+        "sqlplan"
+      ],
       "iconPath": [
         {
           "id": "mssql:cloud",