Add instantValidation prop for TextArea (#2355)

## Summary:
- Adds instantValidation prop so there is an option to validate on blur. If instantValidation is false, the error is also cleared on change
- If textarea is required and instantValidation is false, validate whenever the user tabs away from the field

Issue: WB-1781

Next: I'll work on refactoring TextField to a function component first and then will add the same `instantValidation` prop to TextField

## Test plan:
- Instant Validation docs are reviewed (`/?path=/docs/packages-form-textarea--docs#instant%20validation`)
- Instant Validation works as expected (see docs for expected behaviour) (`/?path=/story/packages-form-textarea--instant-validation`)

Author: beaesguerra

Reviewers: beaesguerra, jandrade, marcysutton

Required Reviewers:

Approved By: jandrade

Checks: ✅ Chromatic - Get results on regular PRs (ubuntu-latest, 20.x), ✅ Test / Test (ubuntu-latest, 20.x, 2/2), ✅ Test / Test (ubuntu-latest, 20.x, 1/2), ✅ Lint / Lint (ubuntu-latest, 20.x), ✅ Check build sizes (ubuntu-latest, 20.x), ✅ Chromatic - Build on regular PRs / chromatic (ubuntu-latest, 20.x), ✅ Publish npm snapshot (ubuntu-latest, 20.x), ✅ Prime node_modules cache for primary configuration (ubuntu-latest, 20.x), ⏭️  Chromatic - Skip on Release PR (changesets), ✅ Check for .changeset entries for all changed files (ubuntu-latest, 20.x), ✅ gerald, ⏭️  dependabot

Pull Request URL: #2355

Author: beaesguerra

.changeset/chatty-moles-brush.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/wonder-blocks-form": minor
+---
+
+Adds `instantValidation` prop for TextArea

__docs__/wonder-blocks-form/text-area.stories.tsx

@@ -293,6 +293,99 @@ ErrorFromPropAndValidation.parameters = {
     },
 };
 
+/**
+ * The `instantValidation` prop controls when validation is triggered. Validation
+ * is triggered if the `validate` or `required` props are set.
+ *
+ * It is preferred to set `instantValidation` to `false` so that the user isn't
+ * shown an error until they are done with a field. Note: if `instantValidation`
+ * is not explicitly set, it defaults to `true` since this is the current
+ * behaviour of existing usage. Validation on blur needs to be opted in.
+ *
+ * Validation is triggered:
+ * - On mount if the `value` prop is not empty
+ * - If `instantValidation` is `true`, validation occurs `onChange` (default)
+ * - If `instantValidation` is `false`, validation occurs `onBlur`
+ *
+ * When `required` is set to `true`:
+ * - If `instantValidation` is `true`, the required error message is shown after
+ * a value is cleared
+ * - If `instantValidation` is `false`, the required error message is shown
+ * whenever the user tabs away from the required field
+ */
+export const InstantValidation: StoryComponentType = {
+    args: {
+        validate(value: string) {
+            const emailRegex = /^[^@\s]+@[^@\s.]+\.[^@.\s]+$/;
+            if (!emailRegex.test(value)) {
+                return "Please enter a valid email";
+            }
+        },
+    },
+    render: (args) => {
+        return (
+            <View style={{gap: spacing.small_12}}>
+                <LabelSmall htmlFor="instant-validation-true-not-required">
+                    Validation on mount if there is a value
+                </LabelSmall>
+                <ControlledTextArea
+                    {...args}
+                    id="instant-validation-true-not-required"
+                    value="invalid"
+                />
+                <LabelSmall htmlFor="instant-validation-true-not-required">
+                    Error shown immediately (instantValidation: true, required:
+                    false)
+                </LabelSmall>
+                <ControlledTextArea
+                    {...args}
+                    id="instant-validation-true-not-required"
+                    instantValidation={true}
+                />
+                <LabelSmall htmlFor="instant-validation-false-not-required">
+                    Error shown onBlur (instantValidation: false, required:
+                    false)
+                </LabelSmall>
+                <ControlledTextArea
+                    {...args}
+                    id="instant-validation-false-not-required"
+                    instantValidation={false}
+                />
+
+                <LabelSmall htmlFor="instant-validation-true-required">
+                    Error shown immediately after clearing the value
+                    (instantValidation: true, required: true)
+                </LabelSmall>
+                <ControlledTextArea
+                    {...args}
+                    validate={undefined}
+                    value="T"
+                    id="instant-validation-true-required"
+                    instantValidation={true}
+                    required="Required"
+                />
+                <LabelSmall htmlFor="instant-validation-false-required">
+                    Error shown on blur if it is empty (instantValidation:
+                    false, required: true)
+                </LabelSmall>
+                <ControlledTextArea
+                    {...args}
+                    validate={undefined}
+                    id="instant-validation-false-required"
+                    instantValidation={false}
+                    required="Required"
+                />
+            </View>
+        );
+    },
+    parameters: {
+        chromatic: {
+            // Disabling because this doesn't test anything visual.
+            disableSnapshot: true,
+        },
+    },
+};
+
 /**
  * A required field will have error styling if the field is left blank. To
  * observe this, type something into the field, backspace all the way,