Update docs for TEXTDECODE settings. NFC (#24698)

The behavior for pthreads was changed in #24349 but the docs were not
updated.

Author: sbc100

site/source/docs/tools_reference/settings_reference.rst

@@ -2695,8 +2695,10 @@ TEXTDECODER
 If enabled, use the JavaScript TextDecoder API for string marshalling.
 Enabled by default, set this to 0 to disable.
 If set to 2, we assume TextDecoder is present and usable, and do not emit
-any JS code to fall back if it is missing. In single threaded -Oz build modes,
-TEXTDECODER defaults to value == 2 to save code size.
+any JS code to fall back if it is missing.
+Note: In -Oz builds, the default value of TEXTDECODER is set to 2, to save on
+code size (except when AUDIO_WORKLET is specified, or when `shell` is part
+of ENVIRONMENT since TextDecoder is not available in those environments).
 
 Default value: 1
 

src/settings.js

@@ -1772,8 +1772,10 @@ var EVAL_CTORS = 0;
 // If enabled, use the JavaScript TextDecoder API for string marshalling.
 // Enabled by default, set this to 0 to disable.
 // If set to 2, we assume TextDecoder is present and usable, and do not emit
-// any JS code to fall back if it is missing. In single threaded -Oz build modes,
-// TEXTDECODER defaults to value == 2 to save code size.
+// any JS code to fall back if it is missing.
+// Note: In -Oz builds, the default value of TEXTDECODER is set to 2, to save on
+// code size (except when AUDIO_WORKLET is specified, or when `shell` is part
+// of ENVIRONMENT since TextDecoder is not available in those environments).
 // [link]
 var TEXTDECODER = 1;