Do not use FillChar to initialize records

### 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

NoFillCharOnRecords

### Rule description

Using `FillChar` or `ZeroMemory` to initialize a record can evolve badly if one adds a managed field to the record. If the Delphi version supports it, it is suggested to use `:= Default(T)` instead.

This was suggested as part of #149, but is too dependent on using a recent Delphi version. Making it a separate rule is more adequate.

### Rationale

Using `FillChar` on a managed field can skip a refcount `Release` and result in large memory leaks.