ws: tests and fixes

This started out as regression tests for the `curl_ws_recv()` and
`curl_ws_send()` implementation and ended up with a bugfix, additional
protocol validation and minor logging improvements.

- Fix reset of fragmented message decoder state when a PING/PONG is
  received in between message fragments.

- Fix undefined behavior (applying zero offset to null pointer) in
  curl_ws_send() when the given buffer is NULL.

- Detect invalid overlong PING/PONG/CLOSE frames.
- Detect invalid fragmented PING/PONG/CLOSE frames.
- Detect invalid sequences of fragmented frames.

  - a) A continuation frame (0x80...) is received without any ongoing
    fragmented message.
  - b) A new fragmented message is started (0x81/0x01/0x82/0x02...)
    before the ongoing fragmented message has terminated.

- Made logs for invalid opcodes easier to understand.
- Moved noisy logs to the `CURL_TRC_WS` log level.
- Unified the prefixes for WebSocket log messages: `[WS] ...`

- Add env var `CURL_WS_FORCE_ZERO_MASK` in debug builds.

  - If set, it forces the bit mask applied to outgoing payloads to
    0x00000000, which effectively means the payload is not masked at
    all. This drastically simplifies defining the expected `<protocol>`
    data in test cases.

- 2700: Frame types
- 2701: Invalid opcode 0x3
- 2702: Invalid opcode 0xB
- 2703: Invalid reserved bit RSV1 _(replaces 2310)_
- 2704: Invalid reserved bit RSV2
- 2705: Invalid reserved bit RSV3
- 2706: Invalid masked server message
- 2707: Peculiar frame sizes _(part. replaces 2311)_
- 2708: Automatic PONG
- 2709: No automatic PONG _(replaces 2312)_
- 2710: Unsolicited PONG
- 2711: Empty PING/PONG/CLOSE
- 2712: Max sized PING/PONG/CLOSE
- 2713: Invalid oversized PING _(replaces 2307)_
- 2714: Invalid oversized PONG
- 2715: Invalid oversized CLOSE
- 2716: Invalid fragmented PING
- 2717: Invalid fragmented PONG
- 2718: Invalid fragmented CLOSE
- 2719: Fragmented messages _(part. replaces 2311)_
- 2720: Fragmented messages with empty fragments
- 2721: Fragmented messages with interleaved pong
- 2722: Invalid fragmented message without initial frame
- 2723: Invalid fragmented message without final frame

- 2305: curl_ws_recv() loop reading three larger frames
  - This test involuntarily sent an invalid sequence of opcodes (0x01...,0x01...,0x81...) , but neither libcurl nor the test caught this! The correct sequence was tested in 2311 (0x01...,0x00...,0x80...). See below for 2311.
  - Validation of the opcode sequence was added to libcurl and is now tested in 2723.
  - Superseded by 2719 (fragmented message) and 2707 (large frames).
- 2307: overlong PING payload
  - The tested PING payload length check was actually missing, but the test didn't catch this since it involuntarily sent an invalid opcode (0x19... instead of 0x89...) so that the expected error occurred, but for the wrong reason.
  - Superseded by 2713.
- 2310: unknown reserved bit set in frame header
  - Superseded by 2703 and extended by 2704 and 2705.
- 2311: curl_ws_recv() read fragmented message
  - Superseded by 2719 (fragmented message) and 2707 (large frames).
- 2312: WebSockets no auto ping
  - Superseded by 2709.

- No tests for `CURLOPT_WRITEFUNCTION`.
- No tests for sending of invalid frames/fragments.

Closes #17136

tests/data/Makefile.am

@@ -258,8 +258,8 @@ test2100 test2101 test2102 \
 \
 test2200 test2201 test2202 test2203 test2204 test2205 \
 \
-test2300 test2301 test2302 test2303 test2304 test2305 test2306 test2307 \
-test2308 test2309 test2310 test2311 test2312 \
+test2300 test2301 test2302 test2303 test2304 test2306 \
+test2308 test2309 \
 \
 test2400 test2401 test2402 test2403 test2404 test2405 test2406 \
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@@ -267,6 +267,10 @@ test2500 test2501 test2502 test2503 \
 \
 test2600 test2601 test2602 test2603 test2604 \
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+test2700 test2701 test2702 test2703 test2704 test2705 test2706 test2707 \
+test2708 test2709 test2710 test2711 test2712 test2713 test2714 test2715 \
+test2716 test2717 test2718 test2719 test2720 test2721 test2722 test2723 \
+\
 test3000 test3001 test3002 test3003 test3004 test3005 test3006 test3007 \
 test3008 test3009 test3010 test3011 test3012 test3013 test3014 test3015 \
 test3016 test3017 test3018 test3019 test3020 test3021 test3022 test3023 \