New rule: `var` arguments should be initialized before the call

### Prerequisites

- [X] This rule has not already been suggested.
- [X] This should be a new rule, not an improvement to an existing rule.
- [X] This rule would be generally useful, not specific to my code or setup.

### Suggested rule title

VarArgumentsShouldBeInitialized

### Rule description

In #127, there was a discussion on whether `var` argument should be considered as initializing a variable. Although `out` arguments should be preferred for that, a confusion in the Delphi compiler (`out` and `var` are processed similarly) has lead some teams to accept initialization through `var`. So, this was suggested as a new rule rather than an improvement or the rule that "variables should be initialized before being used".

This rule states that a variable is "used" when passed as a `var` argument to a function call, so doing so without the variable being initialized should be warned against.

### Rationale

If you do not accept in your code base that initialization could be done via a `var` argument, then the rationale is the same as stating that a variable should be initialized before being used.

It is especially important for record variables, for which the Delphi compiler does not enforce this basic rule!