Per UEFI spec, on CallBack action EFI_BROWSER_ACTION_CHANGING, the return value of...

Per UEFI spec, on CallBack action EFI_BROWSER_ACTION_CHANGING, the return value of ActionRequest will be ignored, but on CallBack action EFI_BROWSER_ACTION_CHANGED, the return value of ActionRequest will be used.
But, EDKII browser still processes the got ActionRequest. And, all HII drivers in EDKII project also returns their expected ActionRequest value on action EFI_BROWSER_ACTION_CHANGING.
Now update the browser to follow the spec, and update all core Hii drivers to keep old working modal.

Update for MdeModulePkg.

Signed-off-by: ydong10
Reviewed-by: lgao4
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12865 6f19259b-4bc3-4df7-8a09-765794883524