Support prioritized entry in ProcessorSlot interface

[sczyh30]

Describe what this PR does / why we need it

Support prioritized entry in ProcessorSlot interface so that each slot can handle requests with priority.

Does this pull request fix one issue?

Related to #207

Describe how you did it

• Refactor ProcessorSlot interface (add a parameter prioritized in entry-related methods)
• Add entryWithPriority methods in SphU (separate from entry method so that it won't be confused with previous entry with args)

Describe how to verify it

This is only a change for interface. Run all test cases to ensure nothing broken.

Special notes for reviews

NONE

[codecov-io]

Codecov Report

Merging #255 into master will increase coverage by 0.63%.
The diff coverage is 81.81%.

@@             Coverage Diff              @@
##             master     #255      +/-   ##
============================================
+ Coverage     51.78%   52.42%   +0.63%     
- Complexity      894      903       +9     
============================================
  Files           150      150              
  Lines          5030     5036       +6     
  Branches        723      723              
============================================
+ Hits           2605     2640      +35     
+ Misses         2110     2077      -33     
- Partials        315      319       +4

Impacted Files	Coverage Δ	Complexity Δ
...e/src/main/java/com/alibaba/csp/sentinel/SphU.java	70.58% <0%> (-9.42%)	12 <0> (ø)
.../sentinel/slots/nodeselector/NodeSelectorSlot.java	94.73% <100%> (ø)	4 <0> (ø)	⬇️
...com/alibaba/csp/sentinel/slots/logger/LogSlot.java	73.33% <100%> (ø)	3 <1> (ø)	⬇️
.../csp/sentinel/slots/block/degrade/DegradeSlot.java	100% <100%> (ø)	3 <0> (ø)	⬇️
...entinel/slotchain/AbstractLinkedProcessorSlot.java	92.85% <100%> (ø)	7 <0> (ø)	⬇️
...sentinel/slots/block/flow/param/ParamFlowSlot.java	76.78% <100%> (ø)	18 <0> (ø)	⬇️
...tinel/slots/clusterbuilder/ClusterBuilderSlot.java	71.42% <100%> (ø)	8 <0> (ø)	⬇️
...ba/csp/sentinel/slots/statistic/StatisticSlot.java	61.11% <100%> (ø)	10 <4> (ø)	⬇️
.../alibaba/csp/sentinel/slots/system/SystemSlot.java	100% <100%> (ø)	3 <0> (ø)	⬇️
.../sentinel/slots/block/authority/AuthoritySlot.java	88.23% <100%> (ø)	7 <0> (ø)	⬇️
... and 6 more

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[CarpenterLee]

LGTM