Added name_starts_with_yaml_object edit field and result field - fixes #1269

[philayres]

Summary

Implements an edit field and result field for name_starts_with_yaml_object.

Edit field

Adds common_templates/edit_fields/_name_starts_with_yaml_object.html.erb, which renders a YAML CodeMirror editor (following the existing pattern used by the JSON edit fields) for yaml_object_* fields backed by a text/varchar column.

Dynamic::FieldEditAs::Handler resolves yaml_object_* fields backed by text/varchar columns to a new yaml_object edit_as field type, handled by Dynamic::FieldEditAs::YamlObject, which validates that submitted text parses as a YAML Hash/Array (raising FphsException otherwise) and persists the original YAML text as-is.

Result field

common_templates/_common_template_result_fields.html.erb parses the stored YAML text via the yaml_parse Handlebars helper and renders it through the existing typeof object structured/collapsible view used for JSON object fields.

Testing

• Unit specs for Dynamic::FieldEditAs::Handler and Dynamic::FieldEditAs::YamlObject
• View specs for the new edit field partial and the result field Handlebars condition
• Jasmine specs for the CodeMirror setup helper and the yaml_parse Handlebars helper
• System spec covering create/edit of a dynamic model field through the CodeMirror editor

Part of #1251.

Fixes #1269