Keep the real error when user code throws, instead of reporting an escaped break

[nohwnd]

Found while looking at #2646. A BeforeAll that throws reports the wrong error, and the real one is discarded:

Where the throw is	Reported
top-level BeforeAll	A 'break' or 'continue' statement with a label that does not match any enclosing loop escaped from your code…
Describe-level BeforeAll	same
inside an It	correct

So someone whose setup failed because a database was down is told their code has a misspelled loop label, and what it actually threw is gone.

Cause

The #2669 guard in Invoke-ScriptBlock:

$flowControlEscaped = $MoveBetweenScopes   # true for user code
try {
    do { ...invoke... } while ($false)
    $flowControlEscaped = $false           # skipped when user code throws
}
finally {
    if ($flowControlEscaped) { throw (New-EscapedFlowControlErrorRecord) }
}

A genuine throw skips the reset, so the finally throws the guard's error record on top of the real exception, and in PowerShell the exception from a finally wins.

Fix

Clear the flag on the error path too. A labelled break/continue escape is not catchable, which is the whole premise of the guard, so the new catch only ever runs for real errors and the guard still works.

Verified all four cases:

top      -> TOP LEVEL ERROR
inner    -> INNER ERROR
intest   -> IN TEST ERROR
label    -> A 'break' or 'continue' statement with a label that does not match...

Two regression tests added next to the existing #2669 ones.

Note

This is not #2646 itself. That one is about the output omitting the test names when a BeforeAll fails, and the result object already contains every test marked Failed — so it is a rendering fix at a different layer, and it is still open.

tst excluding the parallel file is at 2910 passed / 12 failed, identical to main's baseline on the same machine. The P phase is clean apart from the Invoke-InRunspacePool failure that #3004 fixes.

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