Previously the builtins table had a value for every single
OperandScale/Bytecode combination regardless of whether it was valid.
This change makes it so that only valid bytecode handlers are stored in
the builtins table. This prevents placeholders being serialized into the
snapshot (and embedded into the binary) saving 9KB in
CODE_SPACE/OLD_SPACE and 2.5KB in the embedded data as well as 66
entries in the builtins table.

To do this, it generates a new header file bytecodes-builtins-list.h
which is created from the BYTECODE_LIST and OPERAND_SCALE_LIST macros.
Since list macros cannot be used to conditionally generate elements in
the C-preprocessor, this is done by generator executable, compiled from
interpreter/generate-flat-headers.cc.

Additionally the generator creates the flat bytecode list so that it is
transposed from the previous result, i.e. the results are grouped by
bytecode and then operand scale rather than operand scale then bytecode.
This should give better locality for commonly used bytecodes and may
allow less commonly used ExtraWide bytecodes to never be mapped into
memory at all.

The cost to storing the handlers densely is that looking up a handler
now requires a binary search through the builtins table, but this should
only happen during debugging. It is also fixable at least for non-wide
handlers and could be improved for wide ones if the need arises.

Bug: v8:8068
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Iaad22a952e2858f508030c5ddc082f91bf59f667
Reviewed-on: https://chromium-review.googlesource.com/1209304
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55757}