MdePkg/UefiLib: introduce EfiOpenFileByDevicePath()

MdePkg/UefiLib: introduce EfiOpenFileByDevicePath()

The EfiOpenFileByDevicePath() function centralizes functionality from

- MdeModulePkg/Universal/Disk/RamDiskDxe
- NetworkPkg/TlsAuthConfigDxe
- SecurityPkg/VariableAuthenticated/SecureBootConfigDxe
- ShellPkg/Library/UefiShellLib

unifying the implementation and fixing various bugs.

(Ray suggested that we eliminate the special handling of
EFI_FILE_MODE_CREATE in the "OpenMode" input parameter as well. We plan to
implement that separately, under
<https://bugzilla.tianocore.org/show_bug.cgi?id=1074>.)

Cc: Chao Zhang <chao.b.zhang@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Roman Bacik <roman.bacik@broadcom.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1008
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>