Support Dagger and Double Dagger objects

**Background**
Dagger (†) and Double Dagger (‡) are standalone graphical symbols placed freely on the canvas.
Supporting Ketcher issue - https://github.com/epam/ketcher/issues/10472

**Requirements**

1. Indigo should support conversion between KET, CDX, and CDXML.

2. KET should support Dagger and Double Dagger as distinct simple objects and preserve:
the symbol type;
its position on the canvas;
its size.

3. CDX represents these symbols through the Symbol_Type property:
6 — Dagger
7 — Double Dagger

Indigo should convert them to and from the corresponding KET objects.

4. CDXML represents them as graphic symbol objects using:
GraphicType="Symbol"
SymbolType="Dagger" or SymbolType="DoubleDagger"
BoundingBox for the object position and size.

Start by tracing Indigo's existing KET, CDX, and CDXML conversion paths for graphical objects. Add distinct Dagger and Double Dagger handling using the specified symbol types and preserve their position and size; done means round-trip conversion across all three formats retains these properties.

Written by the indexing model from the issue text.