tp+ui: resolve process/thread names for (is_pid)/(is_tid) args

Args produced from an (is_pid)/(is_tid) proto field annotation carried a
resolved upid/utid but were stored as a plain integer, so the UI showed a bare
number with no way to see or group by the process.

A upid/utid is an int with a semantic annotation, not a new primitive type. A
new Variadic type would touch every exhaustive Variadic::Type switch; instead a
side table records the annotation, keeping the args schema and value_type
untouched and leaving room for multiple annotations per key.

trace_processor:
  - New __intrinsic_arg_annotation(key, annotation) table (SQL view
    arg_annotation). An annotation is a property of the key, so each
    (key, annotation) is stored once, not per arg set. AddUpid/AddUtid store
    Variadic::Integer and tag the arg 'upid'/'utid'; the tag threads through
    ArgsTracker / GlobalArgsTracker, which writes each distinct pair once.
  - arg_set_to_json loads the (small) annotation table once and, next to a
    <...>upid/<...>utid arg, emits a companion <...>process_name/<...>thread_name
    resolved from the process/thread table at query time, so always the final
    name. The details panel shows it with no UI-side work.

ui (datagrid): the slice-selection aggregator's args selector exposes the same
companion name key and resolves it by joining arg_annotation on key.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Change-Id: Ibd68b0625dfb88af307c52ca4a6785c99140d0a6