Auto merge of #20431 - talklittle:issues-13234-5600-squashed, r=jdm

TextDecoder: streaming decode, ignoreBOM

<!-- Please describe your changes on the following line: -->
Implement streaming decode and ignoreBOM flag for TextDecoder.

https://encoding.spec.whatwg.org/#dom-textdecoder-decode

https://encoding.spec.whatwg.org/#dom-textdecoder-ignorebom

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #13234 (github issue number if applicable).
- [x] These changes fix #5600 (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because the wpt tests are used for testing:

* /encoding/textdecoder-fatal-streaming.html
* /encoding/textdecoder-streaming.html
* /encoding/textdecoder-ignorebom.html

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<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

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tests/wpt/metadata/encoding/textdecoder-byte-order-marks.html.ini

@@ -1,12 +0,0 @@
-[textdecoder-byte-order-marks.html]
-  type: testharness
-  bug: https://github.com/servo/servo/issues/13233
-  [Byte-order marks: utf-8]
-    expected: FAIL
-
-  [Byte-order marks: utf-16le]
-    expected: FAIL
-
-  [Byte-order marks: utf-16be]
-    expected: FAIL
-

tests/wpt/metadata/encoding/textdecoder-copy.any.js.ini

@@ -1,11 +0,0 @@
-[textdecoder-copy.any.html]
-  type: testharness
-  [Modify buffer after passing it in]
-    expected: FAIL
-
-
-[textdecoder-copy.any.worker.html]
-  type: testharness
-  [Modify buffer after passing it in]
-    expected: FAIL
-

tests/wpt/metadata/encoding/textdecoder-fatal-streaming.html.ini

@@ -1,6 +0,0 @@
-[textdecoder-fatal-streaming.html]
-  type: testharness
-  bug: https://github.com/servo/servo/issues/13234
-  [Fatal flag, streaming cases]
-    expected: FAIL
-

tests/wpt/metadata/encoding/textdecoder-ignorebom.html.ini

@@ -1,15 +0,0 @@
-[textdecoder-ignorebom.html]
-  type: testharness
-  bug: https://github.com/servo/servo/issues/5600
-  [BOM is ignored if ignoreBOM option is specified: utf-8]
-    expected: FAIL
-
-  [BOM is ignored if ignoreBOM option is specified: utf-16le]
-    expected: FAIL
-
-  [BOM is ignored if ignoreBOM option is specified: utf-16be]
-    expected: FAIL
-
-  [The ignoreBOM attribute of TextDecoder]
-    expected: FAIL
-

tests/wpt/metadata/encoding/textdecoder-streaming.html.ini

@@ -1,48 +0,0 @@
-[textdecoder-streaming.html]
-  type: testharness
-  bug: https://github.com/servo/servo/issues/13234
-  [Streaming decode: utf-16le, 1 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16le, 3 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16le, 5 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16be, 1 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16be, 3 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16be, 5 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-8, 1 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-8, 2 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-8, 3 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-8, 4 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-8, 5 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16le, 2 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16le, 4 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16be, 2 byte window]
-    expected: FAIL
-
-  [Streaming decode: utf-16be, 4 byte window]
-    expected: FAIL
-