Support specifying extra VM arguments for the Java Language server

* eglot.el (eglot-java-vmargs): New defcustom.
(eglot-eclipse-jdt): Specify VM arguments.

eglot.el

@@ -3005,6 +3005,15 @@ If NOERROR, return predicate, else erroring function."
 
 ;;; eclipse-jdt-specific
 ;;;
+(defcustom eglot-java-vmargs '("-XX:+UseParallelGC" "-XX:GCTimeRatio=4" "-XX:AdaptiveSizePolicyWeight=90" "-Dsun.zip.disableMemoryMapping=true" "-Xmx1G" "-Xms100m")
+  "Specifies extra VM arguments used to launch the Java Language Server.
+
+Eg. use `-noverify -Xmx1G -XX:+UseG1GC
+-XX:+UseStringDeduplication` to bypass class
+verification,increase the heap size to 1GB and enable String
+deduplication with the G1 Garbage collector"
+  :type '(repeat string))
+
 (defclass eglot-eclipse-jdt (eglot-lsp-server) ()
   :documentation "Eclipse's Java Development Tools Language Server.")
 
@@ -3083,13 +3092,14 @@ If INTERACTIVE, prompt user for details."
       (unless (file-directory-p workspace)
         (make-directory workspace t))
       (cons 'eglot-eclipse-jdt
-            (list (executable-find "java")
-                  "-Declipse.application=org.eclipse.jdt.ls.core.id1"
-                  "-Dosgi.bundles.defaultStartLevel=4"
-                  "-Declipse.product=org.eclipse.jdt.ls.core.product"
-                  "-jar" jar
-                  "-configuration" config
-                  "-data" workspace)))))
+            `(,(executable-find "java")
+              "-Declipse.application=org.eclipse.jdt.ls.core.id1"
+              "-Dosgi.bundles.defaultStartLevel=4"
+              "-Declipse.product=org.eclipse.jdt.ls.core.product"
+              ,@eglot-java-vmargs
+              "-jar" ,jar
+              "-configuration" ,config
+              "-data" ,workspace)))))
 
 (cl-defmethod eglot-execute-command
   ((_server eglot-eclipse-jdt) (_cmd (eql java.apply.workspaceEdit)) arguments)