(core) New Grist Forms styling and field options

Summary:
 - New styling for forms.
 - New field options for various field types (spinner, checkbox, radio buttons, alignment, sort).
 - Improved alignment of form fields in columns.
 - Support for additional select input keyboard shortcuts (Enter and Backspace).
 - Prevent submitting form on Enter if an input has focus.
 - Fix for changing form field type causing the field to disappear.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D4223

app/common/gutil.ts

@@ -175,6 +175,21 @@ export async function firstDefined<T>(...list: Array<() => Promise<T>>): Promise
   return undefined;
 }
 
+/**
+ * Returns the number repesentation of `value`, or `defaultVal` if it cannot
+ * be represented as a valid number.
+ */
+export function numberOrDefault<T>(value: unknown, defaultVal: T): number | T {
+  if (typeof value === 'number') {
+    return !Number.isNaN(value) ? value : defaultVal;
+  } else if (typeof value === 'string') {
+    const maybeNumber = Number.parseFloat(value);
+    return !Number.isNaN(maybeNumber) ? maybeNumber : defaultVal;
+  } else {
+    return defaultVal;
+  }
+}
+
 /**
  * Parses json and returns the result, or returns defaultVal if parsing fails.
  */