add BuildContext class and fix enabled features

Add a BuildContext class to simplify parsing the build context dict, and
fix the parsing of enabledBuildFeatures, which was being parsed as a
list of strings when it's actually a list of dicts like:
[{'name': '<feature_name>'}]

Test: atest build_test_suites_test
Bug: 361605425
Change-Id: I6424c444daf1582e92313c39f43207cb274aa78f
diff --git a/ci/build_test_suites.py b/ci/build_test_suites.py
index deb1f1d..402880c 100644
--- a/ci/build_test_suites.py
+++ b/ci/build_test_suites.py
@@ -24,6 +24,7 @@
 import subprocess
 import sys
 from typing import Callable
+from build_context import BuildContext
 import optimized_targets
 
 
@@ -53,18 +54,9 @@
   any output zip files needed by the build.
   """
 
-  _DOWNLOAD_OPTS = {
-      'test-config-only-zip',
-      'test-zip-file-filter',
-      'extra-host-shared-lib-zip',
-      'sandbox-tests-zips',
-      'additional-files-filter',
-      'cts-package-name',
-  }
-
   def __init__(
       self,
-      build_context: dict[str, any],
+      build_context: BuildContext,
       args: argparse.Namespace,
       target_optimizations: dict[str, optimized_targets.OptimizedBuildTarget],
   ):
@@ -74,18 +66,15 @@
 
   def create_build_plan(self):
 
-    if 'optimized_build' not in self.build_context.get(
-        'enabledBuildFeatures', []
-    ):
+    if 'optimized_build' not in self.build_context.enabled_build_features:
       return BuildPlan(set(self.args.extra_targets), set())
 
     build_targets = set()
     packaging_functions = set()
-    self.file_download_options = self._aggregate_file_download_options()
     for target in self.args.extra_targets:
       if self._unused_target_exclusion_enabled(
           target
-      ) and not self._build_target_used(target):
+      ) and not self.build_context.build_target_used(target):
         continue
 
       target_optimizer_getter = self.target_optimizations.get(target, None)
@@ -102,34 +91,11 @@
     return BuildPlan(build_targets, packaging_functions)
 
   def _unused_target_exclusion_enabled(self, target: str) -> bool:
-    return f'{target}_unused_exclusion' in self.build_context.get(
-        'enabledBuildFeatures', []
+    return (
+        f'{target}_unused_exclusion'
+        in self.build_context.enabled_build_features
     )
 
-  def _build_target_used(self, target: str) -> bool:
-    """Determines whether this target's outputs are used by the test configurations listed in the build context."""
-    # For all of a targets' outputs, check if any of the regexes used by tests
-    # to download artifacts would match it. If any of them do then this target
-    # is necessary.
-    regex = r'\b(%s)\b' % re.escape(target)
-    return any(re.search(regex, opt) for opt in self.file_download_options)
-
-  def _aggregate_file_download_options(self) -> set[str]:
-    """Lists out all test config options to specify targets to download.
-
-    These come in the form of regexes.
-    """
-    all_options = set()
-    for test_info in self._get_test_infos():
-      for opt in test_info.get('extraOptions', []):
-        # check the known list of options for downloading files.
-        if opt.get('key') in self._DOWNLOAD_OPTS:
-          all_options.update(opt.get('values', []))
-    return all_options
-
-  def _get_test_infos(self):
-    return self.build_context.get('testContext', dict()).get('testInfos', [])
-
 
 @dataclass(frozen=True)
 class BuildPlan:
@@ -148,7 +114,7 @@
   """
   args = parse_args(argv)
   check_required_env()
-  build_context = load_build_context()
+  build_context = BuildContext(load_build_context())
   build_planner = BuildPlanner(
       build_context, args, optimized_targets.OPTIMIZED_BUILD_TARGETS
   )