## Description
For filtering the trace output, we currently pass flags like
`-trace_type_checking`, `-trace_execution` etc individually and these
can be passed in a combination.
This PR introduces `-trace_phase` flag that takes a list of the
following options:
- `name_resolution`: Include trace output for the name resolution phase.
- `control_flow_resolution`: Include trace output for the control flow
resolution phase.
- `type_checking`: Include trace output for the type checking phase.
- `unformed_variables_resolution`: Include trace output for the unformed
variables resolution phase.
- `declarations`: Include trace output for printing declarations.
- `execution`: Include trace output for program execution.
- `timing`: Include timing logs indicating the time taken by each phase.
- `all`: Include trace output for all phases.
### Example usage:
```
bazel run //explorer -- <program_location> --trace_file=... -trace_phase=type_checking,execution,declarations
```
Created `explorer/trace_testdata/full_trace.carbon` to test the whole trace and some changes in `explorer/file_test.cpp` to treat `/trace_testdata/` tests differently.
Prabhat Sachdeva