Fix horizontal split view not working (#23889)

* Horizontal splitview sorta working

* remove the old element

* support getting size from model view container

* cleanup

* make splitViewHeight optional

* Update src/sql/azdata.proposed.d.ts

Co-authored-by: Charles Gagnon <chgagnon@microsoft.com>

* fix test

---------

Co-authored-by: Charles Gagnon <chgagnon@microsoft.com>

extensions/schema-compare/src/schemaCompareMainWindow.ts

@@ -451,7 +451,7 @@ export class SchemaCompareMainWindow {
 			this.splitView.addItem(this.diffEditor);
 			this.splitView.setLayout({
 				orientation: 'vertical',
-				splitViewHeight: 800
+				splitViewSize: 800
 			});
 
 			// create a map of the differences to row numbers