(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/client/ui2018/checkbox.ts

@@ -23,6 +23,7 @@ export const cssLabel = styled('label', `
   display: inline-flex;
   min-width: 0px;
   margin-bottom: 0px;
+  flex-shrink: 0;
 
   outline: none;
   user-select: none;

app/client/ui2018/radio.ts

@@ -0,0 +1,25 @@
+import {theme} from 'app/client/ui2018/cssVars';
+import {styled} from 'grainjs';
+
+export const cssRadioInput = styled('input', `
+  appearance: none;
+  width: 16px;
+  height: 16px;
+  margin: 0px !important;
+  border-radius: 50%;
+  background-clip: content-box;
+  border: 1px solid ${theme.checkboxBorder};
+  background-color: ${theme.checkboxBg};
+  flex-shrink: 0;
+  &:hover {
+    border: 1px solid ${theme.checkboxBorderHover};
+  }
+  &:disabled {
+    background-color: 1px solid ${theme.checkboxDisabledBg};
+  }
+  &:checked {
+    padding: 2px;
+    background-color: ${theme.controlPrimaryBg};
+    border: 1px solid ${theme.controlPrimaryBg};
+  }
+`);