Flag incorrect return statements in functions and subs

[TwitchBronBron]

void functions and subs may not have a return value. non-void functions and subs must have a return value. This PR adds the following features:

• diagnostic when return a value from void functions or subs
• diagnostic when missing a return value from non-void functions or subs
• code action for deleting return value
• code action for converting sub to function
• code action for removing as void from function
• code action for removing as <type> from sub