Consider simplifying parenthesized_expression

[DavisVaughan]

tree-sitter-r/grammar.js

Lines 282 to 286 in 4279b69

	parenthesized_expression: $ => withPrec(PREC.BLOCK, seq(
	field("open", $._open_parenthesis),
	repeat(field("body", choice($._expression, $._newline))),
	field("close", $._close_parenthesis)
	)),

• I don't think the $._newline is doing anything. The external scanner consumes newlines proactively when you are within () (unlike { for braced_expression, where it is needed)
• I think we should also limit it to exactly 1 field("body", $._expression), rather than allowing for multiple, since R doesn't actually allow this for parenthesized expressions (note, not optional()! see Kevin's comments below)

[kevinushey]

In addition, () alone is technically a parser error -- R requires there to be exactly one expression within the parentheses. The original definition was motivated by the "permissive" style parser but it sounds like we're moving away from that.