Fix wasienv examples to use InstanceExports, not WasiExports

As indicated by @mvancanneyt in https://gitlab.com/freepascal.org/fpc/pas2js/-/issues/39289#note_2237702957 , the InstanceExports is correct.

demo/wasienv/button/BrowserButton1.lpr

@@ -22,7 +22,7 @@ Type
 function TMyApplication.OnBeforeStart(Sender: TObject;
   aDescriptor: TWebAssemblyStartDescriptor): Boolean;
 begin
-  FWADomBridge.WasiExports:=aDescriptor.Exported;
+  FWADomBridge.InstanceExports:=aDescriptor.Exported;
   Result:=true;
 end;
 

demo/wasienv/fetch/BrowserFetch1.lpr

@@ -22,7 +22,7 @@ Type
 function TMyApplication.OnBeforeStart(Sender: TObject;
   aDescriptor: TWebAssemblyStartDescriptor): Boolean;
 begin
-  FWADomBridge.WasiExports:=aDescriptor.Exported;
+  FWADomBridge.InstanceExports:=aDescriptor.Exported;
   Result:=true;
 end;