fix: coerce multipart initial property values to string (via #5166)

* coerce multipart initial property values to string

* add tests

test/e2e-cypress/static/documents/bugs/5164.yaml

@@ -0,0 +1,23 @@
+openapi: "3.0.0"
+
+paths:
+  /:
+    post:
+      requestBody:
+        required: true
+        content:
+          multipart/form-data:
+            schema:
+              type: object
+              properties:
+                first:
+                  type: object
+                  example:
+                    one: abc
+                    two: 123
+                second:
+                  type: array
+                  items:
+                    type: string
+                  example:
+                  - "hi"

test/e2e-cypress/tests/bugs/5164.js

@@ -0,0 +1,19 @@
+describe("#5164: multipart property initial values", () => {
+  it("should provide correct initial values for objects and arrays", () => {
+    const correctObjectValue = JSON.stringify({
+      "one": "abc",
+      "two": 123
+    }, null, 2)
+
+    cy
+      .visit("?url=/documents/bugs/5164.yaml")
+      .get("#operations-default-post_")
+      .click()
+      .get(".try-out__btn")
+      .click()
+      .get(`.parameters[data-property-name="first"] textarea`)
+      .should("have.value", correctObjectValue)
+      .get(`.parameters[data-property-name="second"] input`)
+      .should("have.value", "hi")
+  })
+})