Re-define ::file-selector-button as tree-abiding

It has been removed from the list of tree-abiding pseudo-elements in 14e0f20,
since w3c/cssw-drafts#12251 removed its definition as element-backed and since
all element-backed pseudo-elements are tree-abiding, but it is probably still
tree-abiding (cf. w3c/cssw-drafts#12271).

Author: cdoublev

lib/values/pseudos.js

@@ -225,6 +225,7 @@ const highlight = {
 
 /**
  * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-checkmark}
+ * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-file-selector-button}
  * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-picker}
  * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-picker-icon}
  * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-slider-fill}
@@ -259,6 +260,7 @@ const treeAbiding = {
         'before': { classes: ['empty'], elements: ['marker'] },
         'checkmark': {},
         'details-content': {},
+        'file-selector-button': {},
         'marker': { classes: indexedNames },
         'picker-icon': {},
         'placeholder': {},
@@ -342,7 +344,6 @@ const classes = {
  * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-field-component}
  * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-field-separator}
  * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-field-text}
- * @see {@link https://drafts.csswg.org/css-forms-1/#selectordef-file-selector-button}
  * @see {@link https://drafts.csswg.org/css-multicol-2/#selectordef-column}
  * @see {@link https://drafts.csswg.org/css-overflow-4/#selectordef-nth-fragment}
  * @see {@link https://drafts.csswg.org/css-scoping-1/#selectordef-slotted}
@@ -370,7 +371,6 @@ const elements = {
         'field-component': {},
         'field-separator': {},
         'field-text': {},
-        'file-selector-button': {},
     },
 }