New command: `terrafmt grep`

[magodo]

This PR integrated hclgrep into the terraform.

Example

terraform-provider-azurerm on  revert_case_sensitivity_containers via 🐹 v1.17.7 took 3s 
💢  terrafmt grep -p "*_test.go" . -- -H -x 'resource azurerm_servicebus_namespace $_ {@*_}' -x 'sku = "Basic"'

####### B5 @ #657
internal/services/eventgrid/eventgrid_event_subscription_resource_test.go:643,3-32:
sku                 = "Basic"

####### B7 @ #715
internal/services/eventgrid/eventgrid_system_topic_event_subscription_resource_test.go:689,3-32:
sku                 = "Basic"

####### B4 @ #281
internal/services/servicebus/servicebus_namespace_resource_test.go:279,3-32:
sku                 = "Basic"

####### B6 @ #323
internal/services/servicebus/servicebus_namespace_resource_test.go:320,3-32:
sku                 = "Basic"

[magodo]

@katbyte Thank you for looking into this!

The naming of the options and the wildcard pattern is inherited from https://github.com/mvdan/gogrep, where the spelling of the "-x", "-g" and "-v" verbs came from Rob Pike's Sam editor command language: https://en.wikipedia.org/wiki/Sam_(text_editor) (also used in the Acme editor).

And you are right, hclgrep/gogrep is not same as grep as they are grepping the AST, which makes their syntax a bit complex. I agree to rename the subcommand from grep to hclgrep, to make it clear for users. For the "address-like" syntax, there is an implemention in https://github.com/minamijoyo/hcledit.

[katbyte]

@magodo I'm not familiar with gogrep, but its popularity is dwarfed by the number of people who use grep/egrep, and we are not grepping go. we are grepping HCL/terraform blocks which is very different from go. Thus I'm not sure why we would be modelling a go tool. The concepts don't exactly match and its not clear how to do things as is evident by the complicated syntax we ended up with here.