docs: Revamp + update internal RPC documentation

[austinvalle]

Module version

v1.12.0

Context

The internal RPC documentation we publish for framework is slightly out-of-date and missing some recent RPC additions:

• MoveResourceState and other refactoring/import related RPCs
• All provider function RPCs
• The upcoming ephemeral resource RPCs in ephemeral: Initial ephemeral resource type implementation #1050

We can either revamp it to make it easier to maintain, or just add/update the RPCs as they are now.

Protocol refs:

• https://github.com/hashicorp/terraform-plugin-go/blob/main/tfprotov5/internal/tfplugin5/tfplugin5.proto
• https://github.com/hashicorp/terraform-plugin-go/blob/main/tfprotov6/internal/tfplugin6/tfplugin6.proto