Form comparison and diffing (Delphi.Forms.Diff)

[darianmiller]

Add a library unit for comparing two TFormFile ASTs and producing a
structured diff. Useful for tools that show form-level changes between
commits, migration auditing, and CI pipelines that need to detect
component additions/removals/renames.

Design

TPropertyChange = record
  ComponentPath: string;   // e.g. 'Form1.Panel1.Button1'
  PropertyName: string;
  OldValue: string;        // preview text from FormValuePreview
  NewValue: string;
end;

TComponentChange = record
  Path: string;            // dot-separated path to the component
  ClassName: string;
  ObjectKind: TObjectKind;
end;

TFormDiff = record
  AddedComponents: TArray<TComponentChange>;
  RemovedComponents: TArray<TComponentChange>;
  ChangedProperties: TArray<TPropertyChange>;
  Identical: Boolean;
end;

class function CompareForms(A, B: TFormFile): TFormDiff;

Matching strategy

Components are matched by name path (e.g. Form1.Panel1.Button1).
A component present in B but not A is "added"; present in A but not B
is "removed". Matched components have their properties compared by name
-- differing values produce a TPropertyChange entry.

This name-based matching works for the common case (same form, different
versions). It does not handle component renames -- that would require
heuristic matching and is out of scope for the initial implementation.

Deliverables

• source/Delphi.Forms.Diff.pas with CompareForms function
• Recursive comparison of component trees by name path
• Property comparison using FormValuePreview for value text
• Add unit to test project .dpr and .dproj
• Tests for: identical forms, added/removed components, changed
  properties, nested component changes, empty forms

Acceptance criteria

• Identical forms produce Identical = True and empty arrays
• Added/removed components detected at all nesting levels
• Changed property values reported with old and new preview text
• Component path accurately reflects nesting hierarchy
• All existing tests still pass