optimize EdgeId.asString()

[javeme]

EdgeId.asString() cost 16% time when call:

1. GraphTx.joinTxEdges() -> Edge.switchOwner() -> Edge.assignId() ->
   EdgeId.length() -> EdgeId.asString()
2. Serializer.parseEdge() -> Vertex.addOut|InEdge() -> EdgeId.hashCode() ->
   EdgeId.asString()

also optimize PropertyKey.newValue() cost 1.3% time:

1. Serializer.parseProperty() -> PropertyKey.newValue() -> Class.newInstance()

about 10% performance improvement.

Change-Id: I07159d6503cc67a63d40a8fab5d7c02a42268986

[codecov]

Codecov Report

Merging #946 into master will increase coverage by 0.02%.
The diff coverage is 84.21%.

@@             Coverage Diff              @@
##             master     #946      +/-   ##
============================================
+ Coverage     71.95%   71.97%   +0.02%     
- Complexity     4679     4686       +7     
============================================
  Files           298      298              
  Lines         22339    22366      +27     
  Branches       3165     3175      +10     
============================================
+ Hits          16073    16098      +25     
+ Misses         4700     4696       -4     
- Partials       1566     1572       +6     

Impacted Files	Coverage Δ	Complexity Δ
...in/java/com/baidu/hugegraph/backend/id/EdgeId.java	80.18% <73.68%> (-0.72%)	40.00 <2.00> (+5.00)	⬇️
...n/java/com/baidu/hugegraph/schema/PropertyKey.java	81.73% <88.88%> (-1.27%)	46.00 <2.00> (+1.00)	⬇️
...va/com/baidu/hugegraph/backend/id/IdGenerator.java	82.20% <100.00%> (ø)	19.00 <0.00> (ø)
...in/java/com/baidu/hugegraph/backend/id/IdUtil.java	84.90% <100.00%> (+1.92%)	22.00 <7.00> (+1.00)
...n/java/com/baidu/hugegraph/structure/HugeEdge.java	74.13% <100.00%> (ø)	75.00 <0.00> (ø)
...a/com/baidu/hugegraph/backend/query/Condition.java	79.67% <0.00%> (ø)	31.00% <0.00%> (ø%)
...om/baidu/hugegraph/api/filter/ExceptionFilter.java	66.66% <0.00%> (+4.30%)	0.00% <0.00%> (ø%)

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