Added the BeyondFacts Lab as a prototype (#1175)

app/SharedTools/I18NSourceText.cs

@@ -0,0 +1,9 @@
+namespace SharedTools;
+
+/// <summary>
+/// A text of T() or TB() which the I18N collector found in a source file.
+/// </summary>
+/// <param name="Offset">Where its literal starts in the file.</param>
+/// <param name="Length">How many characters its literal takes in the file.</param>
+/// <param name="Text">The string the compiler makes of the literal.</param>
+public sealed record I18NSourceText(int Offset, int Length, string Text);