Precise code-coverage, collecting type profile and logging function events
need feedback vectors. This cl allocates feedback vector eagerly when any of
these features are required. When the code-coverage mode changes to anything
other than best case, this scans over the entire heap and allocates feedback
vectors for the required functions.

For best case code coverage we use interrupt budget field on the feedback
cell to infer if a function has executed. We still use the invocation count
on the feedback vector if feedback vector is available.

Bug: v8:8394
Change-Id: Ia0e656aaaa024d6d893a5badafc9a42ce36e9ea3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1601143Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61410}