Use TEST_WARNINGS_OUTPUT_FILE to output warnings to console

### Description of the feature request:

Bazel sets $TEST_WARNINGS_OUTPUT_FILE to a writable file path.
Tests may choose to write warnings to this file, but currently bazel doesn't do anything useful with those warnings.
Please consider emitting some form of summary to the console, such as "such and such tests have such and such warnings"

### Which category does this issue belong to?

CLI

### What underlying problem are you trying to solve with this feature?

Expose test warnings to the user, where these warnings are not severe enough to treat them as failures.

### Which operating system are you running Bazel on?

_No response_

### What is the output of `bazel info release`?

_No response_

### If `bazel info release` returns `development version` or `(@non-git)`, tell us how you built Bazel.

_No response_

### What's the output of `git remote get-url origin; git rev-parse HEAD` ?

```text

```

### Have you found anything relevant by searching the web?

_No response_

### Any other information, logs, or outputs that you want to share?

_No response_

Start by tracing Bazel's test execution and console-reporting paths for TEST_WARNINGS_OUTPUT_FILE. Determine how warning files are produced and where test results are summarized. Done means warnings are surfaced in the console with a useful test-specific summary without treating them as failures.

Written by the indexing model from the issue text.