gccrs: Add HIR lowering support for rest pattern in struct patterns' AST

gccrs: Add HIR lowering support for rest pattern in struct patterns' AST

gcc/rust/ChangeLog:

	* ast/rust-pattern.h (StructPatternElements): Rename has_struct_pattern_etc
	to has_rest_pattern, and has_etc to has_rest to signify presense of rest
	patterns more clearly.
	* ast/rust-pattern.cc (StructPatternElements::as_string): Rename variables
	accordingly.
	* ast/rust-ast-collector.cc: Rename variables accordingly.
	* expand/rust-cfg-strip.cc: Rename variables accordingly.
	* parse/rust-parse-impl.h: Rename variable accordingly.
	* hir/tree/rust-hir-pattern.h (StructPatternElements): Add a boolean to track
	presense of rest pattern.
	* hir/rust-ast-lower-pattern.cc (visit(StructPattern)): Add support for
	lowering rest pattern to HIR.
	* typecheck/rust-hir-type-check-pattern.cc (visit(StructPattern)): Remove
	size check when rest pattern is present.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>