src, inspector: add --inspect-brk option (backport 7.x)

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

src, inspector

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Backport of #8979 to 7.x-staging.

add an --inspect-brk option which breaks on first line of user script. same behavior as old --debug-brk flag.