To obtain SourcePositions for unary and binary operators, this CL
changes the "OneOf" parser rule to produce an Identifier*. Forwarding
this new identifier as callee for a CallExpression enables
"goto Definition" support for operators in the Language Server.

Side note: VSCode won't highlight operators with an underlined font
when hovering with Ctrl pressed. "goto Definition" will work
nonetheless using default F12 or Ctrl-Click.

R=tebbi@chromium.org

Bug: v8:7793
Change-Id: Iada06009e324a3de8c453ec058427049e921a70d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1598690
Auto-Submit: Simon Zünd <szuend@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61263}