SingleSourceField can't be hydrated

[mtruscello]

Describe the bug:
SingleSourceField can't be hydrated, making indirect addresses and code generation impossible.

Pants version:
2.30

OS
Affects all OS.

Additional info
Discovered as part of #22978.

The root cause appears to be that validate_resolved_files is called too early during hydrate_sources.
SingleSourceField has expected_num_files=1. Unless it points to an actual file, the validate_resolved_files call after glob expansion will always results in it matching zero files.
resolve_target and generate_sources aren't called until afterwards, so there's no way for this field type to actually make use of them.