Only add parentheses for lambda expression completions with multiple parameters

[gayanper]

The completion suggestions for lambda actually adds parathesis for single parameters today. Only add the parentheses when there are multiple parameters for lambda expression.

[jdneo]

Looks like in both Eclipse and IntelliJ will only add parentheses when the parameter number is larger than 1. And I didn't find a setting to control that behavior. (Correct me if I'm wrong)

If this is true, we can follow the same behavior.

[gayanper]

Fixed by https://github.com/eclipse/eclipse.jdt.ls/pull/2243