Restore extensions in core (#114921)

* bring back grammar extensions

* fix hygiene

* Revert "pull themes from the marketplace"

This reverts commit 0738f76dac.

extensions/theme-defaults/package.json

@@ -0,0 +1,51 @@
+{
+	"name": "theme-defaults",
+	"displayName": "%displayName%",
+	"description": "%description%",
+	"categories": [ "Themes" ],
+	"version": "1.0.0",
+	"publisher": "vscode",
+	"license": "MIT",
+	"engines": { "vscode": "*" },
+	"contributes": {
+		"themes": [
+			{
+				"id": "Default Dark+",
+				"label": "%darkPlusColorThemeLabel%",
+				"uiTheme": "vs-dark",
+				"path": "./themes/dark_plus.json"
+			},
+			{
+				"id": "Default Light+",
+				"label": "%lightPlusColorThemeLabel%",
+				"uiTheme": "vs",
+				"path": "./themes/light_plus.json"
+			},
+			{
+				"id": "Visual Studio Dark",
+				"label": "%darkColorThemeLabel%",
+				"uiTheme": "vs-dark",
+				"path": "./themes/dark_vs.json"
+			},
+			{
+				"id": "Visual Studio Light",
+				"label": "%lightColorThemeLabel%",
+				"uiTheme": "vs",
+				"path": "./themes/light_vs.json"
+			},
+			{
+				"id": "Default High Contrast",
+				"label": "%hcColorThemeLabel%",
+				"uiTheme": "hc-black",
+				"path": "./themes/hc_black.json"
+			}
+		],
+		"iconThemes": [
+			{
+				"id": "vs-minimal",
+				"label": "%minimalIconThemeLabel%",
+				"path": "./fileicons/vs_minimal-icon-theme.json"
+			}
+		]
+	}
+}