Allow leading zeros in JSON scientific notation

[kristoff3r]

I encountered a JSON file in the wild I couldn't parse using the JSON module, because it had a number with an exponent with a leading zero. According to https://stackoverflow.com/questions/19554972/json-standard-floating-point-numbers this should be allowed.

[stepancheg]

Yep, protoc parser seems to allow it as well:

syntax = "proto2";

message Foo {
    optional float f = 1 [default = 1.0e09];
}

[stepancheg]

Thanks! Merged as 0f1bbc9 with test added.

Released as 2.25.1, although in v2 version there's no JSON or protobuf text format parsing, but it affects .proto parsing.