benchmark: throw on invalid type in fs and webstorage

[irontaek]

In 21 fs and webstorage benchmarks, the default: branch of the type switch
creates new Error('Invalid type') without throwing it. An unknown type then
falls through and benchmarks an undefined path instead of failing.

Before:

$ node benchmark/fs/bench-existsSync.js type=bogus n=10
fs/bench-existsSync.js n=10 type="bogus": 42,410.43975384981

After, the same command throws Error: Invalid type. Every type listed in each
benchmark's config still has a matching case, so valid runs are unchanged.

Disclosure: this change was found by a static check for discarded new Error(...)
expressions and prepared with a coding agent, which also ran the commands above.
I'll handle review feedback myself.

[nodejs-github-bot]

Review requested:

• @nodejs/performance

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