Print non-extension fields by field number order instead of .proto file order.

[copybara-service]

Print non-extension fields by field number order instead of .proto file order.

This will affect both JSON and TextFormat. The serialization order for these two formats is not specified, so switching from .proto file order to field number order should not be breaking.

This does not affect the order of extensions, which are always printed last (even if their field numbers interleave with regular fields.

This change appears to speed up JSON encoding by about 15%:

name                                           old speed               new speed               delta
BM_LoadAdsDescriptor_Upb<NoLayout>              132MB/s ± 2%            129MB/s ±11%     ~             (p=0.841 n=5+5)
BM_LoadAdsDescriptor_Upb<WithLayout>            118MB/s ± 1%            118MB/s ± 2%     ~             (p=0.841 n=5+5)
BM_LoadAdsDescriptor_Proto2<NoLayout>          62.3MB/s ± 2%           62.4MB/s ± 2%     ~             (p=0.841 n=5+5)
BM_LoadAdsDescriptor_Proto2<WithLayout>        61.0MB/s ± 2%           60.1MB/s ± 8%     ~             (p=0.421 n=5+5)
BM_Parse_Upb_FileDesc<UseArena, Copy>           566MB/s ± 1%            572MB/s ± 2%     ~             (p=0.222 n=5+5)
BM_Parse_Upb_FileDesc<UseArena, Alias>          626MB/s ± 1%            620MB/s ± 3%     ~             (p=0.421 n=5+5)
BM_Parse_Upb_FileDesc<InitBlock, Copy>          572MB/s ± 1%            578MB/s ± 2%     ~             (p=0.421 n=5+5)
BM_Parse_Upb_FileDesc<InitBlock, Alias>         636MB/s ± 1%            635MB/s ± 2%     ~             (p=0.841 n=5+5)
BM_Parse_Proto2<FileDesc, NoArena, Copy>        360MB/s ±12%            345MB/s ±14%     ~             (p=0.841 n=5+5)
BM_Parse_Proto2<FileDesc, UseArena, Copy>       692MB/s ± 2%            691MB/s ± 4%     ~             (p=0.548 n=5+5)
BM_Parse_Proto2<FileDesc, InitBlock, Copy>      709MB/s ± 1%            705MB/s ± 2%     ~             (p=0.841 n=5+5)
BM_Parse_Proto2<FileDescSV, InitBlock, Alias>   642MB/s ± 1%            646MB/s ± 1%     ~             (p=0.690 n=5+5)
BM_SerializeDescriptor_Proto2                  1.19GB/s ± 8%           1.22GB/s ± 8%     ~             (p=0.095 n=5+5)
BM_SerializeDescriptor_Upb                      725MB/s ± 1%            732MB/s ± 1%     ~             (p=0.056 n=5+5)
BM_JsonParse_Upb                                187MB/s ± 1%            188MB/s ± 2%     ~             (p=1.000 n=5+4)
BM_JsonParse_Proto2                            18.7MB/s ± 1%           18.6MB/s ± 2%     ~             (p=0.841 n=5+5)
BM_JsonSerialize_Upb                            106MB/s ± 1%            122MB/s ± 1%  +14.65%          (p=0.008 n=5+5)
BM_JsonSerialize_Proto2                        54.0MB/s ± 2%           53.9MB/s ± 3%     ~             (p=1.000 n=5+5)