Investigate flaky and broken WPT fetch/api/abort tests

[npaun]

The test fetch/api/abort/general.any.js contains a number of flaky and failing subtests.

Flaky tests

• Stream errors once aborted, after reading. Underlying connection closed
• Stream errors once aborted. Underlying connection closed.

An example log of them flaking: https://github.com/cloudflare/workerd/actions/runs/15562755101/job/43819049604?pr=4272#step:11:7935
The relevant part is this, which isn't very helpful:

 [AggregateError: Stream errors once aborted, after reading. Underlying connection closed.] {
  [errors]: [
    Error: Timed out
        at PromiseTest.<anonymous> (eval:536:43)
        at async Promise.all (index 48)
        at async RunnerState.validate (harness/harness:59:9)
        at async runTest (harness/harness:258:5)
  ]
} 
 The following tests unexpectedly failed: [
  "Stream errors once aborted, after reading. Underlying connection closed."
] 

Incorrect behaviour (needs investigating)

• Aborting rejects with AbortError
• Aborting rejects with abort reason
• Already aborted signal rejects immediately
• Already aborted signal rejects immediately
• Readable stream synchronously cancels with AbortError if aborted before reading

Signal cloning when a request is cloned

• Signal state is cloned
• Signal on request object should also have abort reason
• Signal on request object

These ones might be improved by enabling request_signal_passthrough and/or enable_request_signal but our behaviour around cloning Requests with abort signals might still be wrong

Error type change

• response.formData() rejects if already aborted

Should be easy but might need a compat flag

The "rejects if already aborted" tests

• response.arrayBuffer() rejects if already aborted
• response.blob() rejects if already aborted
• response.bytes() rejects if already aborted
• response.json() rejects if already aborted
• response.text() rejects if already aborted
• response.formData() rejects if already aborted
• Call text() twice on aborted response

These probably all have the same underlying cause.