Change the way of transferring hcl.Body into the plugin side

[wata727]

Currently, hcl.Body is transferred between the host and the plugin in the same way as hcl.Expression (serialization by source code and start position). However, this way has the problem that the merged body cannot be transferred because the range of the merged body spans multiple files.

The solution is to expose an interface like body.Content to the plugin side and get the body content based on the schema specified by the plugin in advance, instead of transferring the whole body. See hashicorp/hcl#332 (comment)

So we need to change the methods of the Runner interface:

• WalkResourceBlocks
• WalkResources
• WalkModuleCalls
• Backend
• Config
• RootProvider

This change plan is a draft. In fact, it may be affected by Terraform's package internalization.

[wata727]

Fixed in https://github.com/terraform-linters/tflint-plugin-sdk/releases/tag/v0.10.0