gccrs: Refactor hir to avoid raw pointers and unneeded fwd

gccrs: Refactor hir to avoid raw pointers and unneeded fwd

Refactor the hir tree files to remove raw pointer usage and most forward
declarations. Move implementation out of headers and split headers into
smaller and more manageable units.

gcc/rust/ChangeLog:

	* Make-lang.in: Add new files.
	* hir/tree/rust-hir-item.h: Move Item definition and remove
	implementations to their corresponding cc file.
	* hir/tree/rust-hir-expr.h: Move implementation to the corresponding
	cc file.
	* hir/tree/rust-hir-path.h: Likewise.
	* hir/tree/rust-hir-pattern.h: Likewise.
	* hir/tree/rust-hir-stmt.h: Likewise.
	* hir/tree/rust-hir-type.h: Likewise.
	* hir/tree/rust-hir-visitor.h: Likewise.
	* hir/tree/rust-hir.h: Likewise.
	* hir/tree/rust-hir.cc (Crate::Crate): Add implementations from Crate
	and remove ConstGenericParam implementations to move them to their
	own file.
	* hir/tree/rust-hir-attrs.h: New file.
	* hir/tree/rust-hir-bound-abstract.h: New file.
	* hir/tree/rust-hir-bound.h: New file.
	* hir/tree/rust-hir-expr-abstract.h: New file.
	* hir/tree/rust-hir-expr.cc: New file.
	* hir/tree/rust-hir-generic-param.cc: New file.
	* hir/tree/rust-hir-generic-param.h: New file.
	* hir/tree/rust-hir-item.cc: New file.
	* hir/tree/rust-hir-literal.h: New file.
	* hir/tree/rust-hir-node.h: New file.
	* hir/tree/rust-hir-path.cc: New file.
	* hir/tree/rust-hir-pattern-abstract.h: New file.
	* hir/tree/rust-hir-simple-path.h: New file.
	* hir/tree/rust-hir-stmt.cc: New file.
	* hir/tree/rust-hir-trait-bound.h: New file.
	* hir/tree/rust-hir-type-abstract.cc: New file.
	* hir/tree/rust-hir-type-abstract.h: New file.
	* hir/tree/rust-hir-type-no-bounds.h: New file.
	* hir/tree/rust-hir-type.cc: New file.
	* hir/tree/rust-hir-visibility.h: New file.
	* hir/tree/rust-hir-visitable.h: New file.
	* checks/lints/rust-lint-marklive.h: Use References.
	* hir/rust-ast-lower-expr.cc (ASTLoweringExpr::visit): Reformat
	vectors.
	* hir/rust-hir-dump.cc (Dump::visit): Use reference.
	* typecheck/rust-hir-type-check-struct.cc (TypeCheckStructExpr::resolve):
	Use references.
	* typecheck/rust-tyty-bounds.cc: Likewise.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>