feat(scaffolder): promote formDecorators out of experimental (#34180)

* feat(scaffolder): promote formDecorators out of experimental

Signed-off-by: benjdlambert <ben@blam.sh>

* fix(scaffolder): parse form decorator input through the configured zod schema

Signed-off-by: benjdlambert <ben@blam.sh>

* refactor(scaffolder-backend): emit single formDecorators field on the parameter-schema response

Signed-off-by: benjdlambert <ben@blam.sh>

* feat(scaffolder): promote form decorator blueprints to public API

Signed-off-by: benjdlambert <ben@blam.sh>

---------

Signed-off-by: benjdlambert <ben@blam.sh>

.changeset/scaffolder-backend-form-decorators.md

@@ -0,0 +1,8 @@
+---
+'@backstage/plugin-scaffolder-backend': minor
+---
+
+The template parameter schema response now exposes a `formDecorators` field
+instead of `EXPERIMENTAL_formDecorators`. Templates that still declare
+`spec.EXPERIMENTAL_formDecorators` are read transparently and surfaced under
+the new field.

.changeset/scaffolder-common-form-decorators.md

@@ -0,0 +1,7 @@
+---
+'@backstage/plugin-scaffolder-common': minor
+---
+
+Promote the `formDecorators` field on the `Template` spec out of experimental.
+The previous `EXPERIMENTAL_formDecorators` field continues to work and is
+kept as a deprecated alias.

.changeset/scaffolder-form-decorator-api-public.md

@@ -0,0 +1,7 @@
+---
+'@backstage/plugin-scaffolder': minor
+---
+
+Promoted `formDecoratorsApiRef`, `ScaffolderFormDecoratorsApi`,
+`DefaultScaffolderFormDecoratorsApi`, and `formDecoratorsApi` from `@alpha`
+to `@public`.

.changeset/scaffolder-form-decorator-input-schema.md

@@ -0,0 +1,8 @@
+---
+'@backstage/plugin-scaffolder': patch
+---
+
+Form decorator input is now parsed against the zod schema configured on the
+decorator before the decorator runs, so defaults declared via `.default()`
+are applied and invalid input is reported through the error API instead of
+silently passing through.

.changeset/scaffolder-form-decorators.md

@@ -0,0 +1,7 @@
+---
+'@backstage/plugin-scaffolder': patch
+---
+
+The template wizard now reads form decorators from the new
+`spec.formDecorators` field on a template, falling back to the deprecated
+`spec.EXPERIMENTAL_formDecorators` for templates that have not been migrated.

.changeset/scaffolder-react-form-decorator-public.md

@@ -0,0 +1,6 @@
+---
+'@backstage/plugin-scaffolder-react': minor
+---
+
+Promoted `FormDecoratorBlueprint` and `ScaffolderFormDecorator` from `@alpha`
+to `@public`.