fix: make ecforceEx return a result which include is request allow and explain

[imp2002]

Fix: #304

Fix: #305

How get explain?

e = new Enforcer("examples/rbac_model.conf", "examples/rbac_policy.csv", true);

EnforceResult enforceResult = e.enforceEx(sub, obj, act);
// or
EnforceResult enforceResult = e.enforceExWithMatcher(matcher, sub, obj, act);

enforceResult.getExplain();

And it does not affect previous instructions and code, when you don't need a explain.

boolean result = e.enforce(sub, obj, act);

[casbin-bot]

@tangyang9464 please review

[codecov-commenter]

Codecov Report

Merging #308 (6d14a79) into master (c61f3e4) will decrease coverage by 0.15%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #308      +/-   ##
==========================================
- Coverage   69.56%   69.41%   -0.16%     
==========================================
  Files          47       48       +1     
  Lines        2185     2197      +12     
  Branches      407      407              
==========================================
+ Hits         1520     1525       +5     
- Misses        550      556       +6     
- Partials      115      116       +1     

Impacted Files	Coverage Δ
...n/java/org/casbin/jcasbin/main/SyncedEnforcer.java	67.42% <ø> (ø)
...in/java/org/casbin/jcasbin/main/EnforceResult.java	46.15% <46.15%> (ø)
...ain/java/org/casbin/jcasbin/main/CoreEnforcer.java	78.01% <100.00%> (-0.44%)	⬇️
src/main/java/org/casbin/jcasbin/util/Util.java	59.37% <0.00%> (+1.04%)	⬆️

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[github-actions]

🎉 This PR is included in version 1.31.1 🎉

The release is available on:

• GitHub release
• v1.31.1

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