Support bracketed function call in function definition

[Pangoraw]

The following syntax:

function (f(a, b))
end

was interpreted as an anonymous function with 1 argument of name f(a,b).
This commits allows this syntax as a function f with two arguments.

This happened to me in the following case where the references to a
where resolved as global a (instead of as an argument):

function (a + b)
    a
end

Before (LanguageServer on neovim)

After (LanguageServer on neovim, highlighting by setting the cursor on the second b)

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[c42f]

Oh I just randomly came across this PR.

I had soo much trouble with the many allowed forms of function in JuliaSyntax.jl So I share your pain :-)