Add ArgumentCompleter snippets (PowerShell#1946)

* Define snippet named 'ArgumentCompleterAttribute with ScriptBlock'

* Define snippet named 'IArgumentCompleter Class'

* Define snippet named 'ArgumentCompleterAttribute ScriptBlock'

Author: travisclagrone

snippets/PowerShell.json

@@ -1025,5 +1025,62 @@
             "}$0"
         ],
         "description": "Pester - It block"
+    },
+    "ArgumentCompleterAttribute with ScriptBlock": {
+        "prefix": "completer-attribute",
+        "body": [
+            "[ArgumentCompleter({",
+            "\t[OutputType([System.Management.Automation.CompletionResult])]  # zero to many",
+            "\tparam(",
+            "\t\t[string] \\$CommandName,",
+            "\t\t[string] \\$ParameterName,",
+            "\t\t[string] \\$WordToComplete,",
+            "\t\t[System.Management.Automation.Language.CommandAst] \\$CommandAst,",
+            "\t\t[System.Collections.IDictionary] \\$FakeBoundParameters",
+            "\t)",
+            "\t",
+            "\t${0:$TM_SELECTED_TEXT}",
+            "})]"
+        ],
+        "description": "ArgumentCompleter parameter attribute with script block definition"
+    },
+    "ArgumentCompleterAttribute ScriptBlock": {
+        "prefix": "completer-scriptblock",
+        "body": [
+            "{",
+            "\t[OutputType([System.Management.Automation.CompletionResult])]  # zero to many",
+            "\tparam(",
+            "\t\t[string] \\$CommandName,",
+            "\t\t[string] \\$ParameterName,",
+            "\t\t[string] \\$WordToComplete,",
+            "\t\t[System.Management.Automation.Language.CommandAst] \\$CommandAst,",
+            "\t\t[System.Collections.IDictionary] \\$FakeBoundParameters",
+            "\t)",
+            "\t",
+            "\t${0:$TM_SELECTED_TEXT}",
+            "}"
+        ],
+        "description": "ArgumentCompleter parameter attribute script block definition"
+    },
+    "IArgumentCompleter Class": {
+        "prefix": "completer-class",
+        "body": [
+            "class ${1:ArgumentCompleter} : System.Management.Automation.IArgumentCompleter {",
+            "\t[System.Collections.Generic.IEnumerable[System.Management.Automation.CompletionResult]] CompleteArgument(",
+            "\t\t[string] \\$CommandName,",
+            "\t\t[string] \\$ParameterName,",
+            "\t\t[string] \\$WordToComplete,",
+            "\t\t[System.Management.Automation.Language.CommandAst] \\$CommandAst,",
+            "\t\t[System.Collections.IDictionary] \\$FakeBoundParameters",
+            "\t) {",
+            "\t\t\\$CompletionResults = [System.Collections.Generic.List[System.Management.Automation.CompletionResult]]::new()",
+            "\t\t",
+            "\t\t${0:$TM_SELECTED_TEXT}",
+            "\t\t",
+            "\t\treturn \\$CompletionResults",
+            "\t}",
+            "}"
+        ],
+        "description": "IArgumentCompleter implementation class definition"
     }
 }