Fix printing for term operators that could be both unary and binary

[bowenszhu]

Fix #512

julia> VERSION
v"1.8.5"

(@v1.8) pkg> st -m Symbolics
Status `~/.julia/environments/v1.8/Manifest.toml`
  [0c5d862f] Symbolics v5.0.2

(@v1.8) pkg> st -m SymbolicUtils
Status `~/.julia/environments/v1.8/Manifest.toml`
  [d1185830] SymbolicUtils v1.0.3

julia> using Symbolics

julia> @variables y::LiteralReal
1-element Vector{Num}:
 y

julia> -y
y

A minus sign is missing in the printing result above.

The internal structure of -y is

julia> SymbolicUtils.isterm(Symbolics.value(-y))
true

julia> operation(Symbolics.value(-y))
- (generic function with 507 methods)

julia> arguments(Symbolics.value(-y))
1-element Vector{Any}:
 y

The printing function dispatched for -y is the following one:

SymbolicUtils.jl/src/types.jl

Lines 779 to 800 in ba96757

	function show_call(io, f, args)
	fname = istree(f) ? Symbol(repr(f)) : nameof(f)
	binary = Base.isbinaryoperator(fname)
	if binary
	for (i, t) in enumerate(args)
	i != 1 && print(io, " $fname ")
	print_arg(io, t, paren=true)
	end
	else
	if issym(f)
	Base.show_unquoted(io, nameof(f))
	else
	Base.show(io, f)
	end
	print(io, "(")
	for i=1:length(args)
	print(io, args[i])
	i != length(args) && print(io, ", ")
	end
	print(io, ")")
	end
	end

Here, the function show_call checks if the operation is binary.

However, the - operator is special which could be both unary and binary. show_call doesn't consider the unary case and thus doesn't work in our test case.

This PR resolves this issue.

With this PR, the printing result is corrected

julia> using Symbolics

julia> @variables y::LiteralReal;

julia> -y
-y

[shashi]

@bowenszhu Hey sorry, can you rebase this? 😅