[wgsl]: Clarify attribute Valid Values. (#2924)

* [wgsl]: Clarify attribute Valid Values.

This PR clarifies that the valid values must be either `AbstractInt` or
`i32` instead of the more generate `integer literal`.

Issue #2916

* Review feedback

wgsl/index.bs

@@ -775,7 +775,7 @@ An attribute [=shader-creation error|must not=] be specified more than once per
   </thead>
 
   <tr><td><dfn noexport dfn-for="attribute">`align`</dfn>
-    <td>[=integer literal=], yielding a positive i32
+    <td>[=shader-creation error|Must=] be a positive [=i32=] or [=AbstractInt=] [=integer literal|literal=]
     <td>[=shader-creation error|Must=] only be applied to a member of a [=structure=] type.
 
     [=shader-creation error|Must=] be a power of 2, and [=shader-creation error|must=] satisfy the required-alignment for the member type:
@@ -791,22 +791,22 @@ An attribute [=shader-creation error|must not=] be specified more than once per
 
     See [[#memory-layouts]]
 
-  <tr><td><dfn noexport dfn-for="attribute">`binding`
-    <td>[=integer literal=], yielding a non-negative i32
+  <tr><td><dfn noexport dfn-for="attribute">`binding`</dfn>
+    <td>[=shader-creation error|Must=] be a non-negative [=i32=] or [=AbstractInt=] [=integer literal|literal=]
     <td>[=shader-creation error|Must=] only be applied to a [=resource=] variable.
 
     Specifies the binding number of the resource in a bind [=attribute/group=].
     See [[#resource-interface]].
 
-  <tr><td><dfn noexport dfn-for="attribute">`builtin`
+  <tr><td><dfn noexport dfn-for="attribute">`builtin`</dfn>
     <td>identifier name for a built-in value
     <td>[=shader-creation error|Must=] only be applied to an entry point
     function parameter, entry point return type, or member of a [=structure=].
 
     Declares a built-in value.
     See [[#builtin-values]].
 
-  <tr><td><dfn noexport dfn-for="attribute">`const`
+  <tr><td><dfn noexport dfn-for="attribute">`const`</dfn>
     <td>*None*
     <td>Must only be applied to function declarations.
 
@@ -817,21 +817,21 @@ An attribute [=shader-creation error|must not=] be specified more than once per
     Note: This attribute is used as a notational convention to describe which
     built-in functions can be used in [=creation-time expressions=].
 
-  <tr><td><dfn noexport dfn-for="attribute">`group`
-    <td>[=integer literal=], yielding a non-negative i32
+  <tr><td><dfn noexport dfn-for="attribute">`group`</dfn>
+    <td>[=shader-creation error|Must=] be a non-negative [=i32=] or [=AbstractInt=] [=integer literal|literal=]
     <td>[=shader-creation error|Must=] only be applied to a [=resource=] variable.
 
     Specifies the binding group of the resource.
     See [[#resource-interface]].
 
-  <tr><td><dfn noexport dfn-for="attribute">`id`
-    <td>[=integer literal=], yielding a non-negative i32
+  <tr><td><dfn noexport dfn-for="attribute">`id`</dfn>
+    <td>[=shader-creation error|Must=] be a non-negative [=i32=] or [=AbstractInt=] [=integer literal|literal=]
     <td>[=shader-creation error|Must=] only be applied to an [=override declaration=] of [=scalar=] type.
 
     Specifies a numeric identifier as an alternate name for a
     [=pipeline-overridable=] constant.
 
-  <tr><td><dfn noexport dfn-for="attribute">`interpolate`
+  <tr><td><dfn noexport dfn-for="attribute">`interpolate`</dfn>
     <td>One or two parameters.
 
     The first parameter [=shader-creation error|must=] be an [=interpolation type=].
@@ -844,7 +844,7 @@ An attribute [=shader-creation error|must not=] be specified more than once per
     and [=fragment=] inputs.
     See [[#interpolation]].
 
-  <tr><td><dfn noexport dfn-for="attribute">`invariant`
+  <tr><td><dfn noexport dfn-for="attribute">`invariant`</dfn>
     <td>*None*
     <td>[=shader-creation error|Must=] only be applied to the `position` built-in value.
 
@@ -859,8 +859,8 @@ An attribute [=shader-creation error|must not=] be specified more than once per
     Note: this attribute maps to the `precise` qualifier in HLSL, and the
     `invariant` qualifier in GLSL.
 
-  <tr><td><dfn noexport dfn-for="attribute">`location`
-    <td>[=integer literal=], yielding a non-negative i32
+  <tr><td><dfn noexport dfn-for="attribute">`location`</dfn>
+    <td>[=shader-creation error|Must=] be a non-negative [=i32=] or [=AbstractInt=] [=integer literal|literal=]
     <td>[=shader-creation error|Must=] only be applied to an entry point function parameter, entry point
     return type, or member of a [=structure=] type.
     [=shader-creation error|Must=] only be applied to declarations of [=numeric scalar=] or [=numeric
@@ -871,7 +871,7 @@ An attribute [=shader-creation error|must not=] be specified more than once per
     See [[#input-output-locations]].
 
   <tr><td><dfn noexport dfn-for="attribute">`size`</dfn>
-    <td>[=integer literal=], yielding a positive i32
+    <td>[=shader-creation error|Must=] be a positive [=i32=] or [=AbstractInt=] [=integer literal|literal=]
     <td>[=shader-creation error|Must=] only be applied to a member of a [=structure=] type.
 
     The number of bytes reserved in the struct for this member.