Add snake_case, kebab-case and camelCase functions

[stephen-harris]

A lot of cloud resources have names that generally follow a particular string case convention, when incorporating variables into resource names it would be useful to force it to adopt that case style. You can get some way with that in terraform by using functions like title, lower, replace but it would cleaner to provide those functions.

I created these functions here before I saw the comment in #63 - but I'm happy to port these changes into the terraform repository if that is deemed more appropriate.

[codecov]

Codecov Report

Merging #80 (b0060d2) into main (4a53886) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #80      +/-   ##
==========================================
+ Coverage   70.36%   70.47%   +0.11%     
==========================================
  Files          79       79              
  Lines        6550     6575      +25     
==========================================
+ Hits         4609     4634      +25     
  Misses       1497     1497              
  Partials      444      444              

Impacted Files	Coverage Δ
cty/function/stdlib/string.go	57.36% <100.00%> (+6.45%)	⬆️

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[apparentlymart]

Hi @stephen-harris! Thanks for working on this.

As you anticipated, I'm going to ask that you send these upstream to Terraform instead of here. The surface area of functions in this repository has got quite large and arguably already has some functions that are a little too esoteric, and the Terraform project is better resourced to maintain its large library of functions than I am in this upstream library.

Although I am also a member of the Terraform team at HashiCorp, I'm writing this comment with my "owner of cty" hat on, so a PR in the Terraform repository will need to be discussed among the broader Terraform team to decide if they want to accept it as-is or ask for some naming/design changes; I can't speak on the whole team's behalf here, but FWIW I like the idea and can see the use of it.