Klaus Post
f56cac6381
jwt: Parse standard claims faster (#13821)
* Use structless/allocationless decoding for header (note "typ" isn't used)
* Create custom unmarshal code using jsonparser for StandardClaims.
Before/After:
```
BenchmarkParseJWTStandardClaims-32 4270724 294.0 ns/op 706 B/op 16 allocs/op
BenchmarkParseJWTStandardClaims-32 5634847 214.7 ns/op 544 B/op 9 allocs/op
BenchmarkParseJWTMapClaims-32 2763045 428.6 ns/op 1251 B/op 29 allocs/op
BenchmarkParseJWTMapClaims-32 2839455 410.9 ns/op 1219 B/op 26 allocs/op
```