Port 4b0f9c85

Original Commit Message:

    Our {Vector} template provides both {start} and {begin} methods. They
    return exactly the same value. Since the {begin} method is needed for
    iteration, and is also what standard containers provide, this CL
    switches all uses of the {start} method to use {begin} instead.

    Patchset 1 was auto-generated by using this clang AST matcher:
        callExpr(
            callee(
              cxxMethodDecl(
                hasName("start"),
                ofClass(hasName("v8::internal::Vector")))
            ),
            argumentCountIs(0))

    Patchset 2 was created by running clang-format. Patchset 3 then
    removes the now unused {Vector::start} method.

R=clemensh@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I119532691af31a3db1107c47de8b6f0c84697b5c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1588226Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#61102}