Run provider-supplied edit rules before example code conversion

[guineveresaenger]

This code is required to successfully apply the edit rules needed for pulumi/pulumi-libvirt#426.

It covers the case for when the upstream file's code sections need to be adjusted for code conversion to work.

It adds a complete index file test which tests the entire plainDocsParser function.
In support of https://github.com/pulumi/home/issues/3598.

• Run provider-supplied edit rules before example conversion. Add complete file tests, with and without provider-supplied edits
• clean up tests

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 12 lines in your changes missing coverage. Please review.

Project coverage is 57.44%. Comparing base (1cb7594) to head (c55ae3c).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/tfgen/installation_docs.go	42.85%	10 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2435      +/-   ##
==========================================
+ Coverage   57.43%   57.44%   +0.01%     
==========================================
  Files         369      369              
  Lines       50209    50265      +56     
==========================================
+ Hits        28836    28874      +38     
- Misses      19795    19806      +11     
- Partials     1578     1585       +7     

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