airframe-http: Add a new RxRouter interface for Scala and Scala.js

[xerial]

Add a prototype of new RxRouter interface for supporting Scala.js and Scala 3

[codecov]

Codecov Report

Merging #2689 (507637c) into master (2ac7f2d) will increase coverage by 0.03%.
The diff coverage is 73.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2689      +/-   ##
==========================================
+ Coverage   82.44%   82.47%   +0.03%     
==========================================
  Files         337      339       +2     
  Lines       14249    14341      +92     
  Branches     2293     2297       +4     
==========================================
+ Hits        11747    11828      +81     
- Misses       2502     2513      +11     

Impacted Files	Coverage Δ
...rc/main/scala/wvlet/airframe/http/RxEndpoint.scala	0.00% <0.00%> (ø)
.../src/main/scala/wvlet/airframe/http/RxFilter.scala	0.00% <0.00%> (ø)
...in/scala/wvlet/airframe/http/router/RxRouter.scala	62.96% <62.96%> (ø)
...vm/src/main/scala/wvlet/airframe/http/Router.scala	90.24% <100.00%> (+2.74%)	⬆️

... and 3 files with indirect coverage changes

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