Add option to analyze all VCS changed files

### Prerequisites

- [X] This improvement has not already been suggested.
- [X] This improvement would be generally useful, not specific to my code or setup.

### Engine area

Delphi IDE integration

### Improvement description

A common use case for DelphiLint is to scan changed files before committing them to source control, to ensure that any Sonar issues aren't inadvertently committed. To facilitate this, DelphiLint should add an option to "Analyze VCS Changed Files" in addition to the current "Analyze Active File" and "Analyze All Open Files".

This is a feature SonarLint already has, see IntelliJ:


### Rationale

It can be annoying to open and scan all changed files manually, and it has been proven convenient by its inclusion in SonarLint already.