Add tools/def_navigation.py providing utilities to locate .def symbols
and occurrences, produce definition/reference locations, build hover
Markdown for addresses (property table with format links and modality
labels), and compute workspace edits for renames (only when a
declaration exists). Helpers include def_symbol_at, def_definition_locations,
def_reference_locations, tcl_def_occurrences, all_def_target_locations,
def_rename_edits and def_hover_markdown, plus small formatting helpers.
Also add server/tests/python_tests/test_def_navigation.py exercising
go-to-definition, hover, references and rename behavior between Tcl and
.def files, including use of unsaved text and ensuring undeclared names
are not renamed. Tests assert address property ordering, modality labels,
and correct edit ordering for workspace edits.
Christoph