[2201.7.x] Fix HTTP/2 pseudo headers removal

[TharmiganK]

Purpose

$Subject

Part of: ballerina-platform/ballerina-library#4732

Examples

This will expose the HTTP2 pseudo headers and will map them to the relevant HTTP normal headers. The following shows the mapping:

Pseudo header	HTTP header
:authority	host
:scheme	x-http2-scheme
:path	x-http2-path

We can directly map the host header as a resource parameter:

service on new http:Listener(9090) {

    resource function get host(@http:Header {name: "host"} string? host) returns json {
        return {"hello": host ?: "nil"};
    }
}

Checklist

• Linked to an issue
• Updated the changelog
• Added tests
• Updated the spec
• Checked native-image compatibility

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (aafc895) 81.62% compared to head (2de675c) 81.62%.
Report is 1 commits behind head on 2201.7.x.

Additional details and impacted files

@@             Coverage Diff             @@
##             2201.7.x    #1764   +/-   ##
===========================================
  Coverage       81.62%   81.62%           
  Complexity        577      577           
===========================================
  Files             393      393           
  Lines           21409    21407    -2     
  Branches         4798     4798           
===========================================
- Hits            17475    17474    -1     
- Misses           2937     2938    +1     
+ Partials          997      995    -2     

Files	Coverage Δ
...rina/stdlib/http/transport/contract/Constants.java	100.00% <ø> (ø)
...tdlib/http/transport/contractimpl/common/Util.java	82.33% <100.00%> (-0.09%)	⬇️

... and 3 files with indirect coverage changes

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0.0% Duplication