Move file owners computation into the engine and make lighter (#6790)

The solution used in #5636 though, was heavy-handed. By requesting `TransitiveHydratedTargets`, we fully constructed the graph of dependencies and then later _also_ constructed the dependent graph (in `DependentGraph`). Moreover, fully hydrating the targets meant unnecessarily fully expanding their source globs.

Create a `find_owners` rule that consumes an `OwnersRequest` to compute the owning targets of some sources (and, optionally, their transitive dependents). Moving this logic into an `@rule` allows us to directly consume the symbol_table_contraint, without a wrapping collection (as in #5579).

Additionally, switch back to requesting target adaptor subclasses while building the `DependentGraph`. The graph-validation that use to occur via requesting `TransitiveHydratedTargets` now occurs as an explicit step during construction of a `DependentGraph`. A TODO there explains an existing weakness of change-detection in the engine.

```
./pants --changed-diffspec='49cc12e5cccc6164a2c4aa83c23300ad7254836f^..49cc12e' --changed-include-dependees=direct --glob-expansion-failure=ignore list
```
is 30 percent faster in the pantsbuild pants repo, primarily due to not expanding source globs.

src/python/pants/bin/BUILD

@@ -21,7 +21,6 @@ python_library(
     'src/python/pants/engine/legacy:address_mapper',
     'src/python/pants/engine/legacy:graph',
     'src/python/pants/engine/legacy:parser',
-    'src/python/pants/engine/legacy:source_mapper',
     'src/python/pants/engine:build_files',
     'src/python/pants/engine:fs',
     'src/python/pants/engine:legacy_engine',

src/python/pants/engine/build_files.py

@@ -264,7 +264,7 @@ def create_graph_rules(address_mapper, symbol_table):
   symbol_table_constraint = symbol_table.constraint()
 
   partial_hydrate_struct = functools.partial(hydrate_struct, symbol_table_constraint)
-  partial_hydrate_struct.__name__ = 'hydrate_struct'
+  functools.update_wrapper(partial_hydrate_struct, hydrate_struct)
 
   return [
     # A singleton to provide the AddressMapper.

src/python/pants/engine/legacy/BUILD

@@ -82,16 +82,3 @@ python_library(
     'src/python/pants/util:objects',
   ],
 )
-
-python_library(
-  name='source_mapper',
-  sources=['source_mapper.py'],
-  dependencies=[
-    ':address_mapper',
-    ':graph',
-    'src/python/pants/base:specs',
-    'src/python/pants/build_graph',
-    'src/python/pants/source',
-    '3rdparty/python:six'
-  ]
-)