refactor(generator): deprecate BodyMediaType properties from input model (#5248)

* refactor(generator): dump BodyMediaType property from input

- update input models to adopt the dump of RquestBodyMediaType and BodyMediaType of response
- update logic to deduce BodyMeidaType from content types
- fix missing `x-www-form-urlencoded` in `ToMediaTyoe()` method
- temporary fix missing `BodyMediaType.Binary` handling in `SerializationBuilder`
- refactoring

part of microsoft/typespec#4215

* fix a bug when parsing content type string

* bump latest mgc

* refactor

* adopt upstream change in pagination

* bump `http-client-csharp`

* regen

* clean up

* fix regen

---------

Co-authored-by: Mingzhe Huang (from Dev Box) <[email protected]>
Co-authored-by: Arcturus Zhang <[email protected]>
Co-authored-by: Wei Hu <[email protected]>

Author: 4 people

eng/scripts/Build-Packages.ps1

@@ -1,14 +1,13 @@
 #Requires -Version 7.0
 
-Import-Module "$PSScriptRoot\Constants.ps1" -DisableNameChecking -Force;
-
 param(
     [string] $BuildNumber,
     [string] $Output,
     [switch] $Prerelease,
     [switch] $PublishInternal
 )
 
+$CurrentDotnetFramework = "net9.0";
 $ErrorActionPreference = 'Stop'
 Set-StrictMode -Version 3.0
 $root = (Resolve-Path "$PSScriptRoot/../..").Path.Replace('\', '/')