Toolchain rules: legacy features need to be explicitly enabled to create a working toolchain

When creating a rule-based toolchain, legacy features must be explicitly enabled in order for tool invocations to be correctly constructed. This can be done in one of two ways:

1. List `implies` on a `cc_action_type_config`:
```python
cc_action_type_config(
name = "arm-none-eabi-ar",
action_types = ["@rules_cc//cc/toolchains/actions:ar_actions"],
tools = [":arm-none-eabi-ar_tool"],
implies = [
"@rules_cc//cc/toolchains/features/legacy:archiver_flags",
"@rules_cc//cc/toolchains/features/legacy:linker_param_file",
]
)
```
2. Create a custom feature that implies legacy features across a `cc_toolchain`.
```python
cc_feature(
name = "legacy_features",
args = [],
enabled = True,
feature_name = "force_legacy_features",
implies = [
"@rules_cc//cc/toolchains/features/legacy:archiver_flags",
"@rules_cc//cc/toolchains/features/legacy:linker_param_file",
# ...
"@rules_cc//cc/toolchains/features/legacy:fission_support",
"@rules_cc//cc/toolchains/features/legacy:sysroot",
],
)

cc_toolchain(
name = "my_toolchain",
# ...
toolchain_features = [
"@pico-sdk//bazel/toolchain:legacy_features",
],
)
```

This is a bit of a stumbling block, since it's not exactly obvious which of these legacy features are required to construct a working toolchain, or how to re-implement these features correctly in a way that makes Bazel happy.

There's a few potential paths to pursue here:
1. Have an option on `cc_toolchain` that enables all legacy features.
2. Provide features (or better, raw `cc_args `/`cc_args_list`) that implement the required flags, and either provide guidance on how to comprehensively build a toolchain that includes the required arguments or make the toolchain rules infer the required args if no args are explicitly provided.