Tomas preparing pre-release, you'll just add the following setting:
"php.completion.setterSnippet": "{PROPERTY} = ${NAME};",
Personally, I have setters like the following:
"php.completion.setterSnippet": "{PROPERTY} = ${NAME} ?? throw new InvalidArgumentException();",
or
"php.completion.setterSnippet": "{PROPERTY} = ${NAME};\nreturn {THIS};",