all: Add support for unknown value refinement data to all types

[austinvalle]

Closes #869

Ref: hashicorp/terraform#30937
Ref: hashicorp/terraform-plugin-go#448

---

This PR introduces value refinement support to the basetypes Go package, which allows Framework providers to communicate unknown value refinements to/from Terraform core (first introduced in Terraform 1.6).

Value refinements are additional constraints that can be applied to unknown values in Terraform that can be used to produce known results from unknown values. For example, with value refinements, providers can now indicate specific attributes will "definitely not be null" during PlanResourceChange, which would allow Terraform core to successfully evaluate expressions like count during plan:

resource "examplecloud_thing" "a" {
  # Has a computed attribute (id) where the final value will not be null
}
resource "examplecloud_thing" "b" {
  // Will successfully evaluate during plan with a "not null" refinement on "id"
  count = examplecloud_thing.a.id != null ? 1 : 0
}

Without unknown value refinements, the above config will return an error when running terraform plan:

│ Error: Invalid count argument
│
│ ...
│
│ The "count" value depends on resource attributes that cannot be
│ determined until apply, so Terraform cannot predict how many
│ instances will be created. To work around this, use the -target
│ argument to first apply only the resources that the count depends
│ on.

---

No changes to existing provider code will be necessary as partially unknown values will still evaluate the same as a wholly unknown value today.

TODOs left on this PR

• Design is still under review
• Couple open items to investigate
  • Double check the Dynamic paths with refinements. There shouldn't be any changes needed since it's just a container (and dynamic itself cannot have a refinement)
  • Double check the int vs. float refinements (int attributes could possible receive a floating point number in a refinement, need to determine how we should handle that)
• Website documentation
• Update to use released version of terraform-plugin-go, once that's ready
• Changelogs

[austinvalle]

TODO: update with released version