Java Language server contributions to package.json

This PR provide a JSON schema for JDT 'contribute/javaExtensions'
property. It gives the capability to have completion, hover, validation
for this property inside package.json.

Signed-off-by: azerr <azerr@redhat.com>

Author: angelozerr

package.json

@@ -49,6 +49,12 @@
         "path": "./snippets/java.json"
       }
     ],
+    "jsonValidation": [
+      {
+        "fileMatch": "package.json",
+        "url": "./schemas/package.schema.json"
+      }
+    ],
     "configuration": {
       "type": "object",
       "title": "Java configuration",

schemas/package.schema.json

@@ -0,0 +1,20 @@
+{
+	"$schema": "http://json-schema.org/draft-04/schema#",
+	"title": "Java Language server contributions to package.json",
+	"type": "object",
+	"properties": {
+		"contributes": {
+			"type": "object",
+			"properties": {
+				"javaExtensions": {
+					"type": "array",
+					"markdownDescription": "Java language server extensions",
+					"items": {
+						"type": "string",
+						"description": "Relative path to a Java language server extension JAR file"
+					}
+				}
+			}
+		}
+	}
+}