Keep necessary parentheses on the LHS of a hung binary operation

[sarathfrancis90]

Two parentheses bugs that were fixed once already come back as soon as the expression is long enough to be hung over multiple lines:

-- input
local someVeryLongVariableNameHere = (-someExtremelyLongOperandNameOnTheLeft) ^ someOtherExtremelyLongOperandNameOnTheRight

-- 2.5.2 output: this is now -(a ^ b)
local someVeryLongVariableNameHere = -someExtremelyLongOperandNameOnTheLeft
	^ someOtherExtremelyLongOperandNameOnTheRight

and, with syntax = "Luau":

-- input
local isNegative = someExtremelyLongVariableNameHere ~= nil and (someExtremelyLongVariableNameHereAsWellOkayThenFine :: number) < someExtremelyLongThresholdVariableNameHereTooRight

-- 2.5.2 output: does not parse, `number < ...` is read as a generic type instantiation
local isNegative = someExtremelyLongVariableNameHere ~= nil
	and someExtremelyLongVariableNameHereAsWellOkayThenFine :: number
		< someExtremelyLongThresholdVariableNameHereTooRight

These are the same cases as #623 and #940. check_excess_parentheses handles both correctly, but only if it is told the expression is the LHS of a binop — and the hanging paths never do. hang_binop_expression forwards whatever context the expression as a whole was hung in, and format_hanging_expression_ passes UnaryOrBinary, so the BinaryLHS/BinaryLHSExponent guards never fire once hanging kicks in.

I pulled the context choice into a small helper and used it at each LHS call site. The direction is one-way — these contexts only ever keep more parentheses, never remove them — so the blast radius is small: across the whole test corpus one existing snapshot changed, multiline-expression-comments-1, where (not strictFiltering) now keeps its parentheses like the non-hung (not true) and false case above it already does.

Found this while checking that formatting is a fixed point (format(format(x)) == format(x)) over the test inputs with various configs; the Luau one showed up as StyLua failing to re-read its own output.

Tested with cargo test on each feature in the CI matrix, plus clippy and rustfmt.