[grpc] update to 1.81.1

[Tradias]

• Changes comply with the maintainer guide.
• SHA512s are updated for each updated download.
• The "supports" clause reflects platforms that may be fixed by this new version, or no changes were necessary.
• Any fixed CI baseline and CI feature baseline entries are removed from that file, or no entries needed to be changed.
• All patch files in the port are applied and succeed.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Exactly one version is added in each modified versions file.

[BillyONeal]

All of the cross compiling configurations failed with something like:

D:\a\_work\1\s\scripts\azure-pipelines/../ci.feature.baseline.txt: error: grpc[core,codegen]:x86-windows build failed but was expected to pass
note: if grpc[codegen] succeeds when built with other features but not alone, consider adding `grpc[core,codegen]:x86-windows=combination-fails`
note: if grpc[codegen] always fails, consider adding `grpc[codegen]:x86-windows=feature-fails`, which will mark this test as failing, and remove grpc[codegen] from combined feature testing
note: if some features are required, consider effectively always enabling those parts in portfile.cmake for grpc, or consider adding `grpc[required-feature]=options` to include 'required-feature' in all tests

[...]

[1086/1918] C:\Windows\system32\cmd.exe /C "cd . && "C:\Program Files\CMake\bin\cmake.exe" -E vs_link_exe --msvc-ver=1951 --intdir=CMakeFiles\grpc_cpp_plugin.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100280~1.0\x64\rc.exe --mt=C:\PROGRA~2\WI3CF2~1\10\bin\100280~1.0\x64\mt.exe --manifests  -- C:\PROGRA~2\MICROS~2\18\BUILDT~1\VC\Tools\MSVC\1451~1.362\bin\Hostx64\x86\link.exe  CMakeFiles\grpc_cpp_plugin.dir\src\compiler\cpp_plugin.cc.obj  /out:grpc_cpp_plugin.exe /implib:grpc_cpp_plugin.lib /pdb:grpc_cpp_plugin.pdb /version:0.0 /machine:X86 /opt:ref /opt:icf /pdbcompress /nologo    /debug /INCREMENTAL /subsystem:console  wsock32.lib  ws2_32.lib  crypt32.lib  gdi32.lib  grpc_plugin_support.lib  wsock32.lib  ws2_32.lib  crypt32.lib  gdi32.lib  D:\installed\x86-windows\debug\lib\utf8_range.lib  D:\installed\x86-windows\debug\lib\zd.lib  D:\installed\x86-windows\debug\lib\libprotobufd.lib  D:\installed\x86-windows\debug\lib\utf8_validity.lib  D:\installed\x86-windows\debug\lib\abseil_dll.lib  -ignore:4221  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib && cd ."
FAILED: [code=4294967295] grpc_cpp_plugin.exe

[...]

cpp_plugin.cc.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __thiscall google::protobuf::compiler::CodeGenerator::CodeGenerator(void)" (__imp_??0CodeGenerator@compiler@protobuf@google@@QAE@XZ) referenced in function "public: __thiscall CppGrpcGenerator::CppGrpcGenerator(void)" (??0CppGrpcGenerator@@QAE@XZ)
cpp_plugin.cc.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __thiscall google::protobuf::compiler::CodeGenerator::~CodeGenerator(void)" (__imp_??1CodeGenerator@compiler@protobuf@google@@UAE@XZ) referenced in function "public: virtual __thiscall CppGrpcGenerator::~CppGrpcGenerator(void)" (??1CppGrpcGenerator@@UAE@XZ)
cpp_plugin.cc.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) int __cdecl google::protobuf::compiler::PluginMain(int,char * * const,class google::protobuf::compiler::CodeGenerator const *)" (__imp_?PluginMain@compiler@protobuf@google@@YAHHQAPADPBVCodeGenerator@123@@Z) referenced in function "int __cdecl grpc::protobuf::compiler::PluginMain(int,char * * const,class google::protobuf::compiler::CodeGenerator const *)" (?PluginMain@compiler@protobuf@grpc@@YAHHQAPADPBVCodeGenerator@12google@@@Z)
cpp_plugin.cc.obj : error LNK2001: unresolved external symbol "public: virtual bool __thiscall google::protobuf::compiler::CodeGenerator::HasGenerateAll(void)const " (?HasGenerateAll@CodeGenerator@compiler@protobuf@google@@UBE_NXZ)
cpp_plugin.cc.obj : error LNK2001: unresolved external symbol "public: virtual class std::vector<class google::protobuf::FieldDescriptor const *,class std::allocator<class google::protobuf::FieldDescriptor const *> > __thiscall google::protobuf::compiler::CodeGenerator::GetFeatureExtensions(void)const " (?GetFeatureExtensions@CodeGenerator@compiler@protobuf@google@@UBE?AV?$vector@PBVFieldDescriptor@protobuf@google@@V?$allocator@PBVFieldDescriptor@protobuf@google@@@std@@@std@@XZ)
cpp_plugin.cc.obj : error LNK2001: unresolved external symbol "public: virtual bool __thiscall google::protobuf::compiler::CodeGenerator::GenerateAll(class std::vector<class google::protobuf::FileDescriptor const *,class std::allocator<class google::protobuf::FileDescriptor const *> > const &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class google::protobuf::compiler::GeneratorContext *,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > *)const " (?GenerateAll@CodeGenerator@compiler@protobuf@google@@UBE_NABV?$vector@PBVFileDescriptor@protobuf@google@@V?$allocator@PBVFileDescriptor@protobuf@google@@@std@@@std@@ABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@6@PAVGeneratorContext@234@PAV76@@Z)
grpc_cpp_plugin.exe : fatal error LNK1120: 6 unresolved externals

Should the feature codegen be "supports": "native" or something else?

Thanks for your submission! Drafted due to apparently legitimate build failures.