Revert "Remove the separator characters construct"

This reverts commit 5cd07648fd.

The separators construct is useful as an optimization. It turns out that
constructing a node for every chunk of whitespace in a document causes a
significant performance regression.

Conflicts:
	src/compiler/build_tables/build_lex_table.cc
	src/compiler/grammar.cc
	src/runtime/parser.c

examples/grammars/javascript.cc

@@ -208,13 +208,13 @@ extern const Grammar javascript = Grammar({
           delimited("\""),
           delimited("'") })) },
     { "_line_break", str("\n") },
-    { "_whitespace", pattern("\\s+") },
     { "identifier", pattern("[\\a_$][\\w_$]*") },
     { "number", pattern("\\d+(\\.\\d+)?") },
     { "null", keyword("null") },
     { "true", keyword("true") },
     { "false", keyword("false") },
 })
-    .ubiquitous_tokens({ "comment", "_whitespace", "_line_break" });
+    .ubiquitous_tokens({ "comment", "_line_break" })
+    .separators({ ' ', '\t', '\r' });
 
 }  // namespace tree_sitter_examples