[FIRRTL] Make Grand Central YAML Output use Block Scalar Output

Currently, Grand Central will output multiline YAML description strings as one line, e.g., `"foo\nbar\baz"`. However, the LLVM YAML library has support for instead emitting this in "block scala" format: https://llvm.org/docs/YamlIO.html#block-scalars. Change FIRRTL's Grand Central pass to do block scalar output of description strings for better readability of the output YAML.

Once implemented, this will change [this test](https://github.com/llvm/circt/blob/69f8394fb59d88ce976754352df020ecdeac743f/test/Dialect/FIRRTL/SFCTests/GrandCentralInterfaces/Wire.fir#L363) from:

```yaml
- name: sub_vecOfBundle
description: "a vector of a bundle in the submodule with a\nmultiline comment"
dimensions: [ 2 ]
```

To something like:

```yaml
- name: sub_vecOfBundle
description: |-
a vector of a bundle in the submodule with a
multiline comment
dimensions: [ 2 ]
```

This should be implemented using LLVM's YAML library support for block scalars, i.e., this likely requires implementing `BlockScalarTraits` for all `X` that have a description that should have multiline output.

Start with the FIRRTL Grand Central pass and the linked Wire.fir test, especially the YAML output around line 363. Read LLVM's YAML block scalar documentation and inspect the description-bearing types that the pass serializes. Done means multiline descriptions use block scalar output and the test expectation matches the new readable YAML form.

Written by the indexing model from the issue text.