fix: Fix ephemeral focus being taken twice (#2521)

## The basics

- [x] I [validated my changes](https://developers.google.com/blockly/guides/contribute/samples#making_and_verifying_a_change)

## The details
### Resolves

Fixes #2514
Fixes #2515

### Proposed Changes

This updates the custom field implementations for `field-sldier` and `field-angle` to use new functionality introduced in RaspberryPiFoundation/blockly#9051.

### Reason for Changes

The regressions reported in #2514 and #2515 were introduced due to the custom fields introducing a scenario where _both_ widget and drop-down divs attempted to take ephemeral focus. This isn't allowed currently as core's `FocusManager` has no tie breaking functionality for ephemeral focus, so the second attempt to request it throws a runtime failure.

The functionality introduced in RaspberryPiFoundation/blockly#9051 allows the custom fields to, through `FieldInput`, disable the automatic ephemeral focus management for `FieldInput`'s inline editor (which uses widget div) so that the custom fields' drop-down div editors can properly take focus, instead.

### Test Coverage

This has been manually tested locally.

Automated tests are, unfortunately, non-trivial here since verifying focus-related behavior (at least through user interactions) requires a working DOM and is very tricky to make work with Node.js. These are tests that would likely be better suited via webdriver, instead. #2527 has been filed to track this work.

### Documentation

No additional documentation is needed here.

### Additional Information

This requires RaspberryPiFoundation/blockly#9051 in order to work.

Author: BenHenning

plugins/field-angle/src/field_angle.ts

@@ -206,11 +206,13 @@ export class FieldAngle extends Blockly.FieldNumber {
   // eslint-disable-next-line @typescript-eslint/naming-convention
   protected override showEditor_(e?: Event) {
     // Mobile browsers have issues with in-line textareas (focus & keyboards).
+    // Also, don't let the parent take ephemeral focus since the drop-down div
+    // below will handle it, instead.
     const noFocus =
       Blockly.utils.userAgent.MOBILE ||
       Blockly.utils.userAgent.ANDROID ||
       Blockly.utils.userAgent.IPAD;
-    super.showEditor_(e, noFocus);
+    super.showEditor_(e, noFocus, false);
 
     const editor = this.dropdownCreate();
     Blockly.DropDownDiv.getContentDiv().appendChild(editor);

plugins/field-slider/src/field_slider.ts

@@ -102,8 +102,9 @@ export class FieldSlider extends Blockly.FieldNumber {
   protected showEditor_(e?: Event, quietInput?: boolean) {
     // Always quiet the input for the super constructor, as we don't want to
     // focus on the text field, and we don't want to display the modal
-    // editor on mobile devices.
-    super.showEditor_(e, true);
+    // editor on mobile devices. Also, don't let the parent take ephemeral focus
+    // since the drop-down div below will handle it, instead.
+    super.showEditor_(e, true, false);
 
     // Build the DOM.
     const editor = this.dropdownCreate_();