Use richer `previewtypes.Parameter` for `wsbuilder`. This is a pre-requirement to adding dynamic parameter validation.
The richer type contains more information than the `db` parameter, so the conversion is lossless.
This PR extracts dynamic parameter rendering logic from
coderd/parameters.go into a new coderd/dynamicparameters package. Partly
for organization and maintainability, but primarily to be reused in
`wsbuilder` to be leveraged as validation.
