Move fis widgets SQL into scalar functions

Add fis_wdg_* table functions for dashboard widgets and wire them into
FuchsDatabase.sqlproj; update the invoice list procs accordingly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Fuchs_Database/dbo/Functions/fis_wdg_requestsforinvoice.sql

@@ -0,0 +1,18 @@
+-- =============================================
+-- Description:	Dashboard widget 'wdg_requestsforinvoice' (Aufträge zur Rechnungsstellung).
+--              Called from [dbo].[fis_widgets].[sql] as: SELECT * FROM [dbo].[fis_wdg_requestsforinvoice]()
+-- =============================================
+CREATE FUNCTION [dbo].[fis_wdg_requestsforinvoice]()
+RETURNS TABLE
+AS
+RETURN
+(
+    SELECT rfi.[Id]
+         , [Nummer] = rfi.[ExternalId]
+         , [Auftrag] = rfi.[Name]
+         , [Arbeit erledigt am] = FORMAT(rfi.[workdoneat], 'dd.MM.', 'de')
+         , [Freigegeben am] = FORMAT(rfi.[ReleasedAt], 'dd.MM.', 'de')
+         , [Kunde] = c.[name]
+      FROM [dbo].[fds__fn_requestsforinvoice]() AS rfi
+           LEFT JOIN [dbo].[mfr__companies] AS c ON c.[id] = rfi.[CustomerId]
+);