Fix references to reserved tokenBinding member

Commit 5f45d34 in PR #1661 changed
the definition type of `CollectedClientData/tokenBinding` from
"dict-member" to "dfn" to resolve Bikeshed errors about the member not
existing in the `CollectedClientData` definition.

However, autolinks to the reserved `tokenBinding` member still use the
`{{foo}}` syntax, which is only for IDL types, so the autolinks no
longer resolve. This results in Bikeshed instead pulling these
autolinks as external refs from the spec database instead of internal
refs, which results in an entry being added to the "terms defined
elsewhere" index: "[WEBAUTHN-3] defines the following terms:
tokenBinding". The changed definition type also changes the generated
link anchor from "#dom-collectedclientdata-tokenbinding" to
"#collectedclientdata-tokenbinding".

This fixes these issues by declaring the link anchor explicitly, for
backwards compatibility, and by changing the autolinks to use the
`[=foo=]` syntax for autolinks to "dfn"-type definitions.

This also fixes the following Bikeshed lint:

```
LINT: Unexported dfn that's not referenced locally - did you mean to export it?
<dfn data-dfn-type="dfn" data-dfn-for="CollectedClientData" id="collectedclientdata-tokenbinding" data-lt="tokenBinding" data-noexport="by-default">tokenBinding<a href="#collectedclientdata-tokenbinding" class="self-link"></a></dfn>
<dfn data-dfn-type="dfn" data-dfn-for="CollectedClientData" id="collectedclientdata-tokenbinding" data-lt="tokenBinding" data-noexport="by-default">tokenBinding<a href="#collectedclientdata-tokenbinding" class="self-link"></a></dfn>
```

index.bs

@@ -3714,15 +3714,17 @@ Note: The {{CollectedClientData}} may be extended in the future. Therefore it's
     ::  This OPTIONAL member contains the inverse of the `sameOriginWithAncestors` argument value
         that was passed into the [=internal method=].
 
-    :   \[RESERVED] <dfn dfn>tokenBinding</dfn>
+        <!-- Setting explicit dfn ID (this becomes the fragment part of the anchor URL) for backwards compatibility;
+             without this Bikeshed generates the id "collectedclientdata-tokenbinding". -->
+    :   \[RESERVED] <dfn dfn id="dom-collectedclientdata-tokenbinding">tokenBinding</dfn>
     ::  This OPTIONAL member contains information about the state of the [=Token Binding=] protocol [[!TokenBinding]] used when communicating
         with the [=[RP]=]. Its absence indicates that the client doesn't support token binding
 
-        Note: While [=Token Binding=] was present in Level 1 and Level 2 of WebAuthn, its use is not expected in Level 3. The {{CollectedClientData/tokenBinding}} field is reserved so that it will not be reused for a different purpose.
+        Note: While [=Token Binding=] was present in Level 1 and Level 2 of WebAuthn, its use is not expected in Level 3. The [=CollectedClientData/tokenBinding=] field is reserved so that it will not be reused for a different purpose.
 
         <div dfn-type="dict-member" dfn-for="TokenBinding">
             :   <dfn>status</dfn>
-            ::  This member SHOULD be a member of {{TokenBindingStatus}} but [=client platforms=] MUST ignore unknown values, treating an unknown value as if the {{CollectedClientData/tokenBinding}} [=map/exist|member does not exist=]. When known, this member is one of the following:
+            ::  This member SHOULD be a member of {{TokenBindingStatus}} but [=client platforms=] MUST ignore unknown values, treating an unknown value as if the [=CollectedClientData/tokenBinding=] [=map/exist|member does not exist=]. When known, this member is one of the following:
 
                 <div dfn-type="enum-value" dfn-for="TokenBindingStatus">
                     :   <dfn>supported</dfn>