Make it easier to start XML language server with suspend

[xorye]

Currently, in order to run vscode-xml with the language server starting with set suspend=y, we must uncomment and comment source code here:

vscode-xml/src/javaServerStarter.ts

Lines 27 to 29 in 35d4af9

	params.push('-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=1054,quiet=y');
	// suspend=y is the default. Use this form if you need to debug the server startup code:
	//params.push('-agentlib:jdwp=transport=dt_socket,server=y,address=1054');

which isn't very user friendly.

I suggest creating a new launch config that sets an environment variable to determine suspend=y or suspend=n.