Fix the order problem of SentinelGatewayFilter and other bugs

[sczyh30]

Describe what this PR does / why we need it

Fix some problems in API gateway adapter common and SC Gateway adapter module.

Does this pull request fix one issue?

Fixes #764

Describe how you did it

• Fix the empty value matching bug in GatewayParamParser.
• There might be some problems when handling Spring @Order annotation in Spring Cloud Gateway, so here I added Ordered support for Spring Cloud Gateway filter. By default the order is HIGHEST_PRECEDENCE. (Related to Question about the order of SentinelGatewayFilter in Spring Cloud Gateway #764, cc @fangjian0423)

Describe how to verify it

Run the test cases and demo.

Special notes for reviews

NONE

[codecov-io]

Codecov Report

Merging #937 into master will increase coverage by <.01%.
The diff coverage is 63.63%.

@@             Coverage Diff              @@
##             master     #937      +/-   ##
============================================
+ Coverage     42.54%   42.55%   +<.01%     
- Complexity     1441     1442       +1     
============================================
  Files           310      310              
  Lines          8993     8998       +5     
  Branches       1222     1222              
============================================
+ Hits           3826     3829       +3     
- Misses         4698     4701       +3     
+ Partials        469      468       -1

Impacted Files	Coverage Δ	Complexity Δ
...apter/gateway/common/param/GatewayParamParser.java	74.66% <40%> (ø)	27 <0> (ø)	⬇️
...inel/adapter/gateway/sc/SentinelGatewayFilter.java	35.48% <83.33%> (+8.56%)	4 <2> (+1)	⬆️
...m/alibaba/csp/sentinel/log/DateFileLogHandler.java	54.54% <0%> (-3.04%)	6% <0%> (-1%)
...ava/com/alibaba/csp/sentinel/node/ClusterNode.java	100% <0%> (+4.76%)	8% <0%> (+1%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7dd20dd...0900ee5. Read the comment docs.

[cdfive]

LGTM