Add Line Spacing (LineHeight) support to font designer and rendering pipeline

[Copilot]

The LineHeight property existed in the RDL data model (Style.cs, StyleInfo.cs) but was never surfaced in the designer UI or applied during rendering.

Changes

Designer UI (RdlDesign)

• FontCtl.cs and StyleTextCtl.cs: Added a Line Height row with a combo box (preset values 8pt–72pt, plus free text), and an fx expression button for dynamic expressions. Controls are added programmatically after InitializeComponent() to avoid .resx modifications.
• Reads/writes LineHeight XML node on load/save, validates input via DesignerUtility.ValidateSize, and resets dirty flag in Apply().
• Added FontCtl_Show_InvalidLineHeight string resource for the validation error.

Rendering

PageDrawing.cs (screen/print):

• When si.LineHeight > 0, delegates to new DrawStringWithLineHeight() which word-wraps text into lines via GetWrappedLines() and draws each line with the configured spacing. Vertical alignment (top/middle/bottom) is computed from total line height.

RenderPdf_iTextSharp.cs (PDF):

• lineSpacing = si.LineHeight > 0 ? si.LineHeight : si.FontSize — used for both line startY offset and all vertical-alignment calculations.

<!-- Example: RDL Style node with LineHeight set -->
<Style>
  <FontFamily>Arial</FontFamily>
  <FontSize>10pt</FontSize>
  <LineHeight>18pt</LineHeight>
</Style>

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add Font > Line spacing callback</issue_title>
<issue_description>Is your feature request related to a problem? Please describe.
Im currently frustrated on not having an option to Change Line spacing. besides the font. and paddings
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add Font > Line spacing callback #265

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