GameStudio: edit System.Guid properties in the property grid

[Nicogo1705]

PR Details

Guid members on components/assets previously fell through to the read-only
ObjectPropertyTemplateProvider fallback and rendered as a non-editable "Guid" row in the
property grid — there was no way to set them from Game Studio at all.

This PR adds a proper Guid editor, plus a few usability layers on top:

Editing — a GuidPropertyTemplateProvider (TypeMatchTemplateProvider, so it also covers
Nullable<Guid>) mirroring the string editor: a TextBox bound through a new GuidToString
value converter. No registration code needed: providers declared in
DefaultPropertyTemplateProviders.xaml are auto-registered, and the default OverrideRule.Some
takes precedence over the read-only fallback.

Commit-time validation — invalid text is passed through by ConvertBack, so the
strongly-typed node setter throws, TextBoxBase raises TextToSourceValueConversionFailed, and
the attached TextBoxPropertyValueValidationBehavior (same pattern as the UFile editor) plays
the red error adorner while the text reverts to the source value. The stored value can never be
corrupted.

Ghost template — while the editor has focus, the typed prefix is completed inline with the
remaining 0000…-0000 pattern in faint text (via a new GuidTemplateRemainder converter), so
the missing length and dash positions are visible at a glance.

Input mask (GuidInputMaskBehavior) —

• hex input is regrouped live as 8-4-4-4-12, dashes inserted automatically (the caret hops past
  a freshly inserted dash);
• deletions are not fought: backspacing a dash does not re-append it;
• input is capped at the full 36-char template (MaxLength), replacing a selection still works;
• pasted {guid} / (guid) forms are unwrapped;
• non-hex content turns the text red immediately (purely visual, nothing is blocked or
  rewritten — commit-time validation does the hard reject).

Before: a [DataMember] public Guid MyId property shows a non-editable row displaying "Guid".
After: the value is editable as text with format guidance, auto-formatting and live feedback.

Related Issue

No linked issue — quality-of-life editor feature; Guid properties on user components were
previously impossible to set from Game Studio.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have built and run the editor to try this change out.

[Nicogo1705]