Update MappingConverter to correctly write the Matcher as C# code

[StefH]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 49 lines in your changes missing coverage. Please review.

Project coverage is 86.56%. Comparing base (95573ee) to head (d37d1b3).
Report is 1 commits behind head on master.

Files	Patch %	Lines
....Matchers.CSharpCode/Matchers/CSharpCodeMatcher.cs	0.00%	8 Missing ⚠️
src/WireMock.Net/Matchers/JSONPathMatcher.cs	20.00%	8 Missing ⚠️
src/WireMock.Net/Serialization/MappingConverter.cs	75.75%	2 Missing and 6 partials ⚠️
src/WireMock.Net/Matchers/NotNullOrEmptyMatcher.cs	0.00%	7 Missing ⚠️
....Net.Tests/Serialization/CustomPathParamMatcher.cs	0.00%	4 Missing ⚠️
...Net/Authentication/AzureADAuthenticationMatcher.cs	0.00%	3 Missing ⚠️
src/WireMock.Net/Matchers/GraphQLMatcher.cs	0.00%	3 Missing ⚠️
src/WireMock.Net/Matchers/MimePartMatcher.cs	50.00%	3 Missing ⚠️
src/WireMock.Net/Matchers/ProtoBufMatcher.cs	0.00%	3 Missing ⚠️
src/WireMock.Net/Matchers/ContentTypeMatcher.cs	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1152      +/-   ##
==========================================
- Coverage   86.58%   86.56%   -0.02%     
==========================================
  Files         427      429       +2     
  Lines       23959    24200     +241     
==========================================
+ Hits        20744    20948     +204     
- Misses       2314     2350      +36     
- Partials      901      902       +1     

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