This replaces all left-over uses of {WasmGraphBuilder::Buffer} with
proper alternatives (e.g. using {base::SmallVector} instead).

R=clemensb@chromium.org

Change-Id: I2607ce7e2638a1bb35daccbb5b38382d5b62a430
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1859626Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64285}