In gdbbjit's event handler, we return early if code_type is not
JIT_CODE. Unfortunately, in all CodeLinePosInfo event, we memset the
struct, so code_type is always BYTE_CODE, so no line information was
getting saved.

Drive-by clean up to aggregate initialize JitCodeEvent. Since the
initializer list is empty, all members are value-initialized, and in
this case, zero-initialized.

Bug: v8:12035
Change-Id: I67df2688f13fafbb0806546568eb2574ac8d5e2e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3071909Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76179}