Avoid relying on old, non-standard tree-sitter regex feature

grammar.js

@@ -172,7 +172,7 @@ module.exports = grammar({
       repeat($._compound_statement_item)
     ),
 
-    preproc_directive: $ => /#[ \t]*\a\w*/,
+    preproc_directive: $ => /#[ \t]*[a-zA-Z]\w*/,
     preproc_arg: $ => token(prec(-1, repeat1(choice(/./, '\\\n')))),
 
     // Main Grammar
@@ -749,7 +749,7 @@ module.exports = grammar({
       '>')
     ),
 
-    identifier: $ => /[\a_][\a\d_]*/,
+    identifier: $ => /[a-zA-Z_]\w*/,
 
     true: $ => token(prec(1, choice('TRUE', 'true'))),
     false: $ => token(prec(1, choice('FALSE', 'false'))),

src/grammar.json

@@ -711,7 +711,7 @@
     },
     "preproc_directive": {
       "type": "PATTERN",
-      "value": "#[ \\t]*\\a\\w*"
+      "value": "#[ \\t]*[a-zA-Z]\\w*"
     },
     "preproc_arg": {
       "type": "TOKEN",
@@ -3874,7 +3874,7 @@
     },
     "identifier": {
       "type": "PATTERN",
-      "value": "[\\a_][\\a\\d_]*"
+      "value": "[a-zA-Z_]\\w*"
     },
     "true": {
       "type": "TOKEN",