Clean up resolver internal APIs. (pex-tool#1420)

Kill ~unused resolve and rename resolve_multi to resolve.
Eliminate ResolvedDistribution alias in favor of InstalledDistribution
which better reflects the shap of the distribution (not a wheel, but an
installed wheel). Fix test-use fallout.

Work towards pex-tool#1401.
Closes pex-tool#969

pex/bin/pex.py

@@ -31,7 +31,7 @@
 from pex.pex_builder import CopyMode, PEXBuilder
 from pex.pip import ResolverVersion
 from pex.platforms import Platform
-from pex.resolver import Unsatisfiable, parsed_platform, resolve_from_pex, resolve_multi
+from pex.resolver import Unsatisfiable, parsed_platform, resolve, resolve_from_pex
 from pex.tracer import TRACER
 from pex.typing import TYPE_CHECKING
 from pex.variables import ENV, Variables
@@ -1024,7 +1024,7 @@ def to_python_interpreter(full_path_or_basename):
                     )
             else:
                 with TRACER.timed("Resolving requirements."):
-                    resolveds = resolve_multi(
+                    resolveds = resolve(
                         requirements=reqs,
                         requirement_files=options.requirement_files,
                         constraint_files=options.constraint_files,

pex/pip.py

@@ -20,7 +20,7 @@
 from textwrap import dedent
 
 from pex import dist_metadata, third_party
-from pex.common import atomic_directory, is_script, safe_mkdtemp
+from pex.common import atomic_directory, safe_mkdtemp
 from pex.compatibility import urlparse
 from pex.dist_metadata import ProjectNameAndVersion
 from pex.distribution_target import DistributionTarget
@@ -51,6 +51,7 @@
         Mapping,
         Optional,
         Protocol,
+        Sequence,
         Tuple,
         Union,
     )
@@ -96,8 +97,8 @@ def for_value(cls, value):
 class PackageIndexConfiguration(object):
     @staticmethod
     def _calculate_args(
-        indexes=None,  # type: Optional[List[str]]
-        find_links=None,  # type: Optional[List[str]]
+        indexes=None,  # type: Optional[Sequence[str]]
+        find_links=None,  # type: Optional[Iterable[str]]
         network_configuration=None,  # type: Optional[NetworkConfiguration]
     ):
         # type: (...) -> Iterator[str]
@@ -171,8 +172,8 @@ def _calculate_env(
     def create(
         cls,
         resolver_version=None,  # type: Optional[ResolverVersion.Value]
-        indexes=None,  # type: Optional[List[str]]
-        find_links=None,  # type: Optional[List[str]]
+        indexes=None,  # type: Optional[Sequence[str]]
+        find_links=None,  # type: Optional[Iterable[str]]
         network_configuration=None,  # type: Optional[NetworkConfiguration]
     ):
         # type: (...) -> PackageIndexConfiguration