replaceSync() and replace() combined two distinct failure conditions into a single check with a single error message, causing the "non-constructed" message to appear even when the sheet was constructed but mid-replacement.

Changes

• CSSStyleSheet-impl.js: Split the !this._constructed || this._disallowModification guard into two separate checks in both replaceSync() and replace(), each with an accurate message:
  • Non-constructed → "Cannot call replaceSync/replace on non-constructed CSSStyleSheet."
  • Modification in progress → "The stylesheet is currently being modified." (consistent with #checkModificationAllowed())

// Before
if (!this._constructed || this._disallowModification) {
  throw DOMException.create(this._globalObject, [
    "Cannot call replaceSync on non-constructed CSSStyleSheet.",
    "NotAllowedError"
  ]);
}

// After
if (!this._constructed) {
  throw DOMException.create(this._globalObject, [
    "Cannot call replaceSync on non-constructed CSSStyleSheet.",
    "NotAllowedError"
  ]);
}
if (this._disallowModification) {
  throw DOMException.create(this._globalObject, [
    "The stylesheet is currently being modified.",
    "NotAllowedError"
  ]);
}

• MediaList-impl.js: Fix typo "spec-complaint" → "spec-compliant" in comment.

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