Keycode generation doc fix (#31493)

Fixes a typo in the key generator readme.

Updated the examples in the readme to reflect that the examples were for physical key codes, where we're actually talking about logical key codes there.

dev/tools/gen_keycodes/README.md

@@ -56,18 +56,21 @@ checked in.
 
 ## Key Code ID Scheme
 
-In order to provide keys with unique ID codes, Flutter uses a scheme to assign
-codes which keeps us out of the business of minting new codes ourselves.
+In order to provide logical keys with unique ID codes, Flutter uses a scheme
+to assign logical key codes which keeps us out of the business of minting new
+codes ourselves. This only applies to logical key codes: Flutter's
+physical key codes are just defined as USB HID codes.
 
-The codes are meant to be opaque to the user, and should never be unpacked for
-meaning, since the code scheme could change at any time, and the meaning is
-likely to be retrievable in a more reliable and correct manner from the API.
+The logical codes are meant to be opaque to the user, and should never be
+unpacked for meaning, since the code scheme could change at any time, and the
+meaning is likely to be retrievable in a more reliable and correct manner from
+the API.
 
 However, if you are porting Flutter to a new platform, you should follow the
-following guidelines for specifying key codes.
+following guidelines for specifying logical key codes.
 
-The key code is a 37-bit integer in a namespace that we control and define. It
-has values in the following ranges.
+The logical key code is a 37-bit integer in a namespace that we control and
+define. It has values in the following ranges.
 
   - **0x00 0000 0000 - 0x0 0010 FFFF**: For keys that generate Unicode
     characters when pressed (this includes dead keys, but not e.g. function keys
@@ -81,9 +84,10 @@ has values in the following ranges.
     key in the US layout outputs a q in normal usage, but its code would be 0x0
     0000 0051 (U+00051 being the code for the uppercase Q).
 
-  - **0x01 0000 0000 - 0x01 FFFF FFFF**: For keys that are defined by the USB HID
-    standard, the key code consists of the 32 bit USB extended usage code. For
-    example, the Enter key would have code 0x0 0007 0028. Only keys that fall
+  - **0x01 0000 0000 - 0x01 FFFF FFFF**: For keys that are defined by the [USB HID
+    standard](https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf),
+    the key code consists of the 32 bit USB extended usage code. For
+    example, the Enter key would have code 0x01 0007 0028. Only keys that fall
     into collections "Keyboard", "Keypad", and "Tablet PC System Controls" are
     considered for this API; for example, a mixing desk with multiple
     collections of volume controls would not be exposed via DOWN and UP events,
@@ -142,23 +146,21 @@ Here are some examples:
 For example, on a French keyboard layout, pressing CAPS LOCK then pressing
 SHIFT + Y would generate the following sequence:
 
-DOWN, code 0x00070039. (CAPS LOCK DOWN)<br>
-UP, code 0x00070039. (CAPS LOCK UP)<br>
-DOWN, code 0x000700E1 (SHIFT DOWN)<br>
-DOWN, code 0x0007001D, string U+00059 (Y DOWN, the code is for the "Z" key, but
-string is the character, "Y")<br>
-UP, code 0x0007001D (Y UP)<br>
-UP, code 0x000700E1 (SHIFT UP)<br>
+DOWN, code 0x0100070039. (CAPS LOCK DOWN)<br>
+UP, code 0x0100070039. (CAPS LOCK UP)<br>
+DOWN, code 0x01000700E1 (LEFT SHIFT DOWN)<br>
+DOWN, code 0x0000000059, string U+00059 (Y DOWN)<br>
+UP, code 0x0000000059 (Y UP)<br>
+UP, code 0x01000700E1 (LEFT SHIFT UP)<br>
 
 Here's another example. On a German keyboard layout, you press ^e (the ^ key is
 at the top left of the keyboard and is a dead key) to produce a “ê”:
 
-DOWN, code 0x00070035 (GRAVE DOWN) Assuming that the keymap maps it to the same
-logical key, it produces no string, because it's a dead key. The HID key is for
-"Keyboard grave accent and tilde" in AT-101 keyboard typical position 1.<br>
-UP, code 0x00070035 (GRAVE UP)<br>
-DOWN, code 0x00070008, string U+000EA (Unicode for ê‬) (E DOWN).<br>
-UP, code 0x00070008. (E UP).<br>
+DOWN, code 0x0000000302 (CIRCUMFLEX DOWN) It produces no string, because it's a dead
+key. The key code is for "Combining circumflex accent U+0302" in Unicode.<br>
+UP, code 0x0000000302 (CIRCUMFLEX UP)<br>
+DOWN, code 0x0000000065, string U+000EA (Unicode for ê‬) (E DOWN).<br>
+UP, code 0x0000000065. (E UP).<br>
 
 It is an important point that even though we’re representing many keys with USB
 HID codes, these are not necessarily the same HID codes produced by the hardware