SSR: Restrict to current selection if any

The selection is also used to avoid unnecessary work, but only to the
file level. Further restricting unnecessary work is left for later.

editors/code/src/lsp_ext.ts

@@ -95,6 +95,7 @@ export interface SsrParams {
     parseOnly: boolean;
     textDocument: lc.TextDocumentIdentifier;
     position: lc.Position;
+    selections: lc.Range[];
 }
 export const ssr = new lc.RequestType<SsrParams, lc.WorkspaceEdit, void>('experimental/ssr');