Implements the change outlined in https://github.com/tc39/ecma262/pull/890,
which has been ratified and pulled into the specification. In particular,
template callsite objects are no longer kept in a global, eternal Map, but
are instead associated with their callsite, which can be collected. This
prevents a memory leak incurred by TaggedTemplate calls.

Changes, summarized:

    - Remove the TemplateMap and TemplateMapShape objects, instead caching
      template objects in the feedback vector.
    - Remove the `hash` member of TemplateObjectDescriptor, and the Equals
      method (used by TemplateMap)
    - Add a new FeedbackSlotKind (kTemplateObject), which behaves similarly
      to FeedbackSlotKind::kLiteral, but prevents eval caching. This ensures
      that a new feedback vector is always created for eval() containing tagged
      templates, even when the CompilationCache is used.
    - GetTemplateObject bytecode now takes a feedback index, and only calls
      into the runtime if the feedback is Smi::kZero (uninitialized).

BUG=v8:3230, v8:2891
R=littledan@chromium.org, yangguo@chromium.org, bmeurer@chromium.org,
rmcilroy@chromium.org

Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I7827bc148d3d93e2b056ebf63dd624da196ad423
Reviewed-on: https://chromium-review.googlesource.com/624564
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51248}