fix(checker): emit precise error when labeled continue/break targets a non-enclosing label

[creazyfrog]

Summary

Fixes #30408

Problem

When a labeled continue or break references a label that is in the same function but not an ancestor (e.g. a forward/sibling reference), TypeScript emits:

TS1107: Jump target cannot cross function boundary.

This message is wrong — no function boundary is crossed. The label lives in the same function; it's just not enclosing the jump statement.

function foo() {
    for (let i = 0; i < 10; i++) {
        continue loopend; // ❌ TS1107 — misleading
    }
    loopend:              // label exists, but is not an ancestor
    console.log('done');
}

Fix

Adds a helper labelExistsInScope(scope, labelName) that walks the children of the enclosing function looking for a matching LabeledStatement (without descending into nested functions).

In checkGrammarBreakOrContinueStatement, before emitting TS1107 at a function boundary, the fix checks whether the named label exists inside the function. If it does, it emits the more accurate diagnostic instead:

• TS1115 for continue: "A 'continue' statement can only jump to a label of an enclosing iteration statement."
• TS1116 for break: "A 'break' statement can only jump to a label of an enclosing statement."

TS1107 is still emitted for the genuine case where the label is in an outer function (truly crossing a function boundary).

Before / After

function foo() {
    for (let i = 0; i < 10; i++) {
        continue loopend;
        //       ~~~~~~~ Before: TS1107 "Jump target cannot cross function boundary"
        //               After:  TS1115 "A 'continue' statement can only jump to a label of an enclosing iteration statement"
    }
    loopend:
    console.log('done');
}

The genuine cross-function case still produces TS1107:

function outer() {
    myLabel:
    function inner() {
        continue myLabel; // TS1107 — correctly reported
    }
}

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