This CL introduces a new contextual 'LanguageSererData'. Its purpose
is to hold all the eagerly calculated data needed to answer
language server requests. The first thing collected are the
definitoins of some IdentifierExpresisons and macro/builtin
call-sites.

Collecting this data is not necessary for normal compilation, so it
is disabled by default and can be enabled via a Torque compiler
option. Since the holder class is a contextual for which no scope
exists during normal compilation, accidental collection of
unnecessary language server data *should* be prevented.

R=tebbi@chromium.org

Bug: v8:7793
Change-Id: Iffcebad4c420a0a51b1ed3c37a37c3475c6ab2e8
Reviewed-on: https://chromium-review.googlesource.com/c/1491594Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59941}