Added formulas from LaTeX code blocks and buttons to copy and save formulas (#1154)

app/MindWork AI Studio/Chat/MarkdownRenderSegment.cs

@@ -0,0 +1,36 @@
+namespace AIStudio.Chat;
+
+/// <summary>
+/// A part of a message which the chat renders on its own, see MarkdownRenderPlan.
+/// </summary>
+/// <param name="type">What the part is.</param>
+/// <param name="start">Where the part starts in the source of its plan.</param>
+/// <param name="length">How long the part is.</param>
+/// <param name="fileStart">Where the block of the part starts in the source, its markers included,
+/// such as the $$ before a formula. A formula finds its file by it, see PlainFileExport.ExtractFiles.</param>
+internal sealed class MarkdownRenderSegment(MarkdownRenderSegmentType type, int start, int length, int fileStart)
+{
+    private string? cachedContent;
+
+    public MarkdownRenderSegmentType Type { get; } = type;
+
+    public int Start { get; } = start;
+
+    public int Length { get; } = length;
+
+    public int FileStart { get; } = fileStart;
+
+    public int RenderKey { get; } = HashCode.Combine(type, start, length);
+
+    public string GetContent(string source)
+    {
+        if (this.cachedContent is not null)
+            return this.cachedContent;
+
+        this.cachedContent = this.Start == 0 && this.Length == source.Length
+            ? source
+            : source.Substring(this.Start, this.Length);
+
+        return this.cachedContent;
+    }
+}