remove use of pkg_resources in external_tool rules (#22048)

Remove use of `pkg_resources` requirements parser in `external_tool` rules in favor of `packaging`.

Author: tdyas

src/python/pants/core/util_rules/external_tool.py

@@ -11,7 +11,7 @@
 from dataclasses import dataclass
 from enum import Enum
 
-from pkg_resources import Requirement
+from packaging.requirements import Requirement
 
 from pants.core.goals.export import (
     ExportedBinary,
@@ -293,9 +293,9 @@ def check_version_constraints(self) -> None:
         if not self.version_constraints:
             return None
         # Note that this is not a Python requirement. We're just hackily piggybacking off
-        # pkg_resource.Requirement's ability to check version constraints.
-        constraints = Requirement.parse(f"{self.name}{self.version_constraints}")
-        if constraints.specifier.contains(self.version):  # type: ignore[attr-defined]
+        # packaging.requirements.Requirement's ability to check version constraints.
+        constraints = Requirement(f"{self.name}{self.version_constraints}")
+        if constraints.specifier.contains(self.version):
             # all ok
             return None