Wording change: Define power prefs & device type using WebIDL enums

Replace definitions for MLContext's device type and power preference
which are used internally only, with the identical WebIDL-defined
MLDeviceType and MLPowerPreference enums.

Fixes #497

index.bs

@@ -796,11 +796,11 @@ Its <a>default allowlist</a> is <code>'self'</code>.
     1. If |options| is a {{GPUDevice}} object,
         1. Set |context|.{{[[contextType]]}} to "[=webgpu-context|webgpu=]".
         1. Set |context|.{{[[deviceType]]}} to "[=device-type-gpu|gpu=]".
-        1. Set |context|.{{[[powerPreference]]}} to "[=power-preference-default|default=]".
+        1. Set |context|.{{[[powerPreference]]}} to {{MLPowerPreference/default}}.
     1. Otherwise,
         1. Set |context|.{{[[contextType]]}} to "[=default-context|default=]".
         1. If |options|["{{deviceType}}"] [=map/exists=], then set |context|.{{[[deviceType]]}} to |options|["{{deviceType}}"]. Otherwise, set |context|.{{[[deviceType]]}} to "[=device-type-cpu|cpu=]".
-        1. If |options|["{{powerPreference}}"] [=map/exists=], then set |context|.{{[[powerPreference]]}} to |options|["{{powerPreference}}"]. Otherwise, set |context|.{{[[powerPreference]]}} to "[=power-preference-default|default=]".
+        1. If |options|["{{powerPreference}}"] [=map/exists=], then set |context|.{{[[powerPreference]]}} to |options|["{{powerPreference}}"]. Otherwise, set |context|.{{[[powerPreference]]}} to {{MLPowerPreference/default}}.
     1. Return |context|.
 </div>
 </details>
@@ -1065,11 +1065,11 @@ The <dfn>device type</dfn> indicates the kind of device used for the context. It
 
 The <dfn>power preference</dfn> indicates preference as related to power consumption. It is one of the following:
 <dl>
-<dt>"<code><dfn data-lt="power-preference-default">default</dfn></code>"</dt>
+<dt>"<code><dfn dfn-for="MLPowerPreference" enum-value>default</dfn></code>"</dt>
 <dd>Let the user agent select the most suitable behavior.</dd>
-<dt>"<code><dfn data-lt="power-preference-high-performance">high-performance</dfn></code>"</dt>
+<dt>"<code><dfn dfn-for="MLPowerPreference" enum-value>high-performance</dfn></code>"</dt>
 <dd>Prioritizes execution speed over power consumption.</dd>
-<dt>"<code><dfn data-lt="power-preference-low-power">low-power</dfn></code>"</dt>
+<dt>"<code><dfn dfn-for="MLPowerPreference" enum-value>low-power</dfn></code>"</dt>
 <dd>Prioritizes power consumption over other considerations such as execution speed.</dd>
 </dl>
 
@@ -1108,7 +1108,7 @@ When the {{[[contextType]]}} is set to [=default-context|default=] with the {{ML
   <div class=algorithm-steps>
     1. If |context|.{{[[contextType]]}} is not "[=webgpu-context|webgpu=]" or "[=default-context|default=]", return false.
     1. If |context|.{{[[deviceType]]}} is not "[=device-type-cpu|cpu=]" or "[=device-type-gpu|gpu=]", return false.
-    1. If |context|.{{[[powerPreference]]}} is not "[=power-preference-default|default=]" or "[=power-preference-high-performance|high-performance=]" or "[=power-preference-low-power|low-power=]", return false.
+    1. If |context|.{{[[powerPreference]]}} is not {{MLPowerPreference/default}} or {{MLPowerPreference/high-performance}} or {{MLPowerPreference/low-power}}, return false.
     1. If the user agent cannot support |context|.{{[[contextType]]}}, |context|.{{[[deviceType]]}} and |context|.{{[[powerPreference]]}}, return false.
     1. Return true;
   </div>