test_runner: refactor snapshots to support multiple files in the same process

test_runner: add context.filePath

This commit adds a filePath getter to the TestContext and SuiteContext classes. This allows a context to be mapped back to the original test file that created it, even if it was imported from another file. This is useful for mapping features like test snapshots to the correct test file. This is also prep work for supporting running test files in the test runner process.

test_runner: refactor snapshots to get file from context

This commit refactors the internals of snapshot tests to get the name of the test file from the test context instead of passing it to the SnapshotManager constructor. This is prep work for supporting running test files in the test runner process.