Reflect new `resource.` address and `_` escaping block in 0.15.4+

[radeksimko]

Background

See hashicorp/terraform#28709

Introduced in v1.0.0 and backported to 0.15.4

Proposal

hcl-lang

• Allow blocks to be targeted with additional address via AdditionalAddress in BlockAddrSchema
  • this additional address is matched against origins, understood in hover or semantic highlighting, but not used in completion

terraform-schema

• AdditionalAddress is added for resource blocks of 0.15.4+
• Introduce _ block with empty BodySchema for now
  • We can consider adding a special field later if this causes a problem during validation, so that it doesn't get flagged up for "unknown attributes" or "unknown blocks" within
  • We can also/instead consider some changes in the body merging logic in hcl-lang so that we can decode attributes and blocks from within _ but the only benefit would be in contexts where we evaluate expressions (such as Show interpolated expression values on hover #495), so the effort vs value added ratio suggests it's not worth doing.

terraform-ls

• Updated to latest hcl-lang
• Updated to latest terrafom-schema