[basic.def.odr] explicitly captured variable is not odr-usable in lambda contract predicate

[abhinavagarwal07]

Subclause: [basic.def.odr]

Issue description

Bullet 4 of the odr-usability rule in [basic.def.odr] paragraph 10 requires the lambda's block scope to be an intervening scope. But a function contract predicate sits in the lambda-declarator, outside the block scope — so this [expr.prim.lambda] example is ill-formed despite its // OK:

void test() {
  int i = 1;
  auto f3 = [i] pre(i > 0) {};   // OK, i is captured explicitly.
}

Only bullet 4 can apply to the intervening lambda scope. i is captured, so the first conjunct holds; the second wants the block scope {} to intervene, but pre(i > 0) precedes {}. So i is not odr-usable.

P2900R14 added a contract-assertion scope to the benign-scope list in p10 but missed bullet 4, which still only knows the block scope. So it rejects this explicit-capture lambda contract predicate just as bullet 4 (CWG 2380) deliberately rejects [=](int k = n) {}.

Proposed resolution

Let bullet 4's second conjunct also accept a contract-assertion scope of the lambda-expression:

 the intervening scope is the lambda scope of a lambda-expression that has a
 simple-capture naming the entity or has a capture-default, and
-the block scope of the lambda-expression
+the block scope of the lambda-expression,
+or a contract-assertion scope [basic.scope.contract] introduced by a function
+contract assertion [dcl.contract.func] of the call operator or operator template
+of that lambda-expression,
 is also an intervening scope.

[=](int k = n) {} stays ill-formed, so CWG 2380 is unaffected.