gccrs: hir: Rename ComoundAssignment getters

gccrs: hir: Rename ComoundAssignment getters

Use more a consistent name.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): Rename method.
	* checks/errors/privacy/rust-privacy-reporter.cc (PrivacyReporter::visit): Rename method.
	* checks/errors/rust-const-checker.cc (ConstChecker::visit): Rename method.
	* checks/errors/rust-unsafe-checker.cc (UnsafeChecker::visit): Rename method.
	* hir/rust-hir-dump.cc (Dump::visit): Rename method.
	* hir/tree/rust-hir-expr.h: Rename method.
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): Rename method.
	* typecheck/rust-tyty.h: Rename method.