It is true that the famous prologue does not appear in the Folio version of Romeo and Juliet. It does, however, appear in the Quarto versions of 1599, 1609 and 1622 in the form we know it, and in the first Quarto of 1597 in somewhat garbled form. In all of the Quarto versions, the Prologue is printed on a separate page before the play starts, and the printer may just have missed it when setting the type. I've included a link to a facsimile of Q2 so you can see what I mean.
Since it is included in all Quarto versions of the plays, and the prologue to Act 2 is not omitted in the Folio, it's probably reasonable to assume that the omission of the general prologue is a printer's error, and was a genuine part of the play.
The authorship of the prologue to Romeo and Juliet is attributed to Shakespeare based on early printed versions of the play. While it doesn't appear in the First Folio of 1623, many scholars believe it was likely part of the original play. The prologue's style and themes are consistent with Shakespeare's work, supporting his authorship.
Romeo and Juliet
reveal the plot, get the groundlings interested, and allow Shakespeare to compose a sonnet
He had already indicated the sad conclusion of the play in the title: The Lamentable Tragedy of Romeo and Juliet.
Either the witches predicitions in Macbeth or the prologue to Romeo and Juliet
No, "Romeo and Juliet" is a play by William Shakespeare and does not have a recurring chorus as in a song or music.
He gives an overview of the plot in the Prologue, but it is extremely vague and general. Most of it you could guess from the title: "The Lamentable Tragedy of Romeo and Juliet."
The prologue of Shakespeare's "Romeo and Juliet" states that the story ultimately results in the tragic ending of two families in Verona, the Capulets and the Montagues, consumed by their longstanding feud.
Shakespeare didn't hold any grudges. He uses the phrase "ancient grudge" in the Prologue to Romeo and Juliet to describe the bad blood which was between the two families of Montague and Capulet.
So that the reader gets a good understanding and so they get hooked and want to read the book. For example, in Shakespeare's "Romeo and Juliet", the prologue briefly foreshadows what will happen, like the two feuding families trying to prevent Romeo and Juliet's love for one another.
The deaths of Romeo and Juliet
Shakespeare uses the word "loins" to figuratively represent a person's private parts. In Romeo and Juliet, for example, he uses the word in the prologue to indicate that Romeo and Juliet are the children of long-time enemy families.
The person that wrote Romeo and Juliet is William Shakespeare.