chore: updated JwtClaims.Builder methods to public

[rahulKQL]

Made JwtClaims#Builder methods public so that the user could create JwtClaims instance.

towards #349

[codecov]

Codecov Report

Merging #396 into master will not change coverage.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #396   +/-   ##
=========================================
  Coverage     79.53%   79.53%           
  Complexity      397      397           
=========================================
  Files            27       27           
  Lines          1803     1803           
  Branches        188      188           
=========================================
  Hits           1434     1434           
  Misses          269      269           
  Partials        100      100

Impacted Files	Coverage Δ	Complexity Δ
...h2_http/java/com/google/auth/oauth2/JwtClaims.java	92.3% <100%> (ø)	8 <0> (ø)	⬇️

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