Make the cache key more precise

[t0yv0]

Make the examples cache key more precise:

• do not look at provider version
• do not look at the entirety of go.mod, only check key package versions
• include MarshallableProviderInfo in the cache
• if go.work is used, still include that as before

[t0yv0]

I think I'm getting decent results with this on AWS in pulumi/pulumi-aws#3737

[codecov]

Codecov Report

Attention: Patch coverage is 67.50000% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 60.04%. Comparing base (f64f0d8) to head (769b4be).

Files	Patch %	Lines
pkg/tfgen/examples_cache.go	67.50%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1793      +/-   ##
==========================================
- Coverage   60.57%   60.04%   -0.53%     
==========================================
  Files         302      309       +7     
  Lines       42213    42623     +410     
==========================================
+ Hits        25569    25594      +25     
- Misses      15173    15559     +386     
+ Partials     1471     1470       -1     

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[iwahbe]

LGTM