Fix Blob.slice() for negative start and inverted ranges

[durvesh1992]

Summary

Blob.slice(start, end) is modeled on the W3C Blob API, where both start and end may be negative (relative to the end of the blob) and an end that precedes start yields an empty blob.

The current implementation handles a negative end but not a negative start:

if (typeof start === 'number') {
  if (start > size) { start = size; }   // only the upper bound is checked
  offset += start;
  size -= start;
  if (typeof end === 'number') {
    if (end < 0) { end = this.size + end; }  // negative end IS handled
    if (end > this.size) { end = this.size; }
    size = end - start;                       // not clamped to >= 0
  }
}

So:

• blob.slice(-100) sets offset to a negative value and makes size larger than the blob, instead of slicing the last 100 bytes.
• blob.slice(200, 100) (end before start) produces a negative size.

Fix

• Normalize a negative start relative to the blob size (Math.max(this.size + start, 0)), mirroring the existing end handling.
• Clamp the resulting size with Math.max(end - start, 0) so an inverted range yields an empty blob.

Test plan

Added tests to Libraries/Blob/__tests__/Blob-test.js for negative start, negative end, and end-precedes-start. The negative-start and inverted-range cases fail before this change (negative offset / negative size) and pass after; existing slice tests and the rest of the suite still pass (8/8). ESLint clean on the changed files.

Changelog:

[General] [Fixed] - Fix Blob.slice() for negative start offsets and inverted ranges

[javache]

Please revert the changes to no-deep-imports

[durvesh1992]

Thanks for the review! Done — I've rebased this branch to drop the no-deep-imports changes (they were unintentionally included from another branch). This PR now only contains the Blob.slice() fix and its tests. The no-deep-imports change is tracked separately in #57373.

[meta-codesync]

@javache has imported this pull request. If you are a Meta employee, you can view this in D110173869.