Previously, macros that returned true for "ShouldBeInlined" were only
compiled if they were called, which made it impossible to
type/semantic check all Torque code (e.g. newly added methods to
structs). One might argue that all code should be tested (and thus
through inlining compiled), but for prototyping, the skipped
compilations were definitely annoying.

As part of this change, added a ShouldGenerateExternalCode method to
declarables (by default returns !ShouldBeInlined) that makes it
possible to suppresses C++ code generation for any method. To
support this at the lowest level, a NullOStream classes is added as
part of this patch.

Finally, added support for generating C++ for passing structs as label
parameters to run previously inlined methods through the
implementation-visitor for non-inlined compilation.

Bug: v8:7793
Change-Id: I8ce23382e12ddc25f46222c25729c82433040a73
Reviewed-on: https://chromium-review.googlesource.com/c/1434378
Commit-Queue: Daniel Clifford <danno@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59134}