Fix unresponsive copy button on instructions modal

This commit fixes the bug where the "Copy" button does not copy when
clicked on download instructions modal (on Linux and macOS).

This commit also introduces several improvements to the UI components
related to copy action and their interaction with the clipboard feature.

It adds more tests to avoid regression of the bugs and improves
maintainability, testability and adherence to Vue's reactive principles.

Changes include:

- Fix non-responsive copy button in the download instructions modal by
  triggering a `click` event in `AppIcon.vue`.
- Improve `TheCodeButtons.vue`:
  - Remove redundant `getCurrentCode` function.
  - Separate components for each button for better separation of
    concerns and higher testability.
  - Use the `gap` property in the flexbox layout, replacing the less
    explicit sibling combinator approach.
- Add `useClipboard` compositional hook for more idiomatic Vue approach
  to interacting with the clipboard.
- Add `useCurrentCode` compositional hook to handle current code state
  more effectively with unified logic.
- Abstract clipboard operations to an interface to isolate
  responsibilities.
- Switch clipboard implementation to the `navigator.clipboard` API,
  moving away from the deprecated `document.execCommand`.
- Move clipboard logic to the presentation layer to conform to
  separation of concerns and domain-driven design principles.
- Improve `IconButton.vue` component to increase reusability with
  consistent sizing.

tests/unit/presentation/components/Code/CodeButtons/Save/Instructions/CodeInstruction.spec.ts

@@ -0,0 +1,96 @@
+import { describe, it, expect } from 'vitest';
+import { shallowMount } from '@vue/test-utils';
+import CodeInstruction from '@/presentation/components/Code/CodeButtons/Save/Instructions/CodeInstruction.vue';
+import { expectThrowsAsync } from '@tests/unit/shared/Assertions/ExpectThrowsAsync';
+import { InjectionKeys } from '@/presentation/injectionSymbols';
+import { Clipboard } from '@/presentation/components/Shared/Hooks/Clipboard/Clipboard';
+import { UseClipboardStub } from '@tests/unit/shared/Stubs/UseClipboardStub';
+import { ClipboardStub } from '@tests/unit/shared/Stubs/ClipboardStub';
+
+const DOM_SELECTOR_CODE_SLOT = 'code';
+const DOM_SELECTOR_COPY_BUTTON = '.copy-button';
+const COMPONENT_TOOLTIP_WRAPPER_NAME = 'TooltipWrapper';
+
+describe('CodeInstruction.vue', () => {
+  it('renders a slot content inside a <code> element', () => {
+    // arrange
+    const expectedSlotContent = 'Example Code';
+    const wrapper = mountComponent({
+      slotContent: expectedSlotContent,
+    });
+    // act
+    const codeSlot = wrapper.find(DOM_SELECTOR_CODE_SLOT);
+    const actualContent = codeSlot.text();
+    // assert
+    expect(actualContent).to.equal(expectedSlotContent);
+  });
+  describe('copy', () => {
+    it('calls copyText when the copy button is clicked', async () => {
+      // arrange
+      const expectedCode = 'Code to be copied';
+      const clipboardStub = new ClipboardStub();
+      const wrapper = mountComponent({
+        clipboard: clipboardStub,
+      });
+      wrapper.vm.codeElement = { textContent: expectedCode } as HTMLElement;
+      // act
+      const copyButton = wrapper.find(DOM_SELECTOR_COPY_BUTTON);
+      await copyButton.trigger('click');
+      // assert
+      const calls = clipboardStub.callHistory;
+      expect(calls).to.have.lengthOf(1);
+      const call = calls.find((c) => c.methodName === 'copyText');
+      expect(call).toBeDefined();
+      const [actualCode] = call.args;
+      expect(actualCode).to.equal(expectedCode);
+    });
+    it('throws an error when codeElement is not found during copy', async () => {
+      // arrange
+      const expectedError = 'Code element could not be found.';
+      const wrapper = mountComponent();
+      wrapper.vm.codeElement = undefined;
+      // act
+      const act = () => wrapper.vm.copyCode();
+      // assert
+      await expectThrowsAsync(act, expectedError);
+    });
+    it('throws an error when codeElement has no textContent during copy', async () => {
+      // arrange
+      const expectedError = 'Code element does not contain any text.';
+      const wrapper = mountComponent();
+      wrapper.vm.codeElement = { textContent: '' } as HTMLElement;
+      // act
+      const act = () => wrapper.vm.copyCode();
+      // assert
+      await expectThrowsAsync(act, expectedError);
+    });
+  });
+});
+
+function mountComponent(options?: {
+  readonly clipboard?: Clipboard,
+  readonly slotContent?: string,
+}) {
+  return shallowMount(CodeInstruction, {
+    global: {
+      provide: {
+        [InjectionKeys.useClipboard as symbol]:
+          () => {
+            if (options?.clipboard) {
+              return new UseClipboardStub(options.clipboard).get();
+            }
+            return new UseClipboardStub().get();
+          },
+      },
+      stubs: {
+        [COMPONENT_TOOLTIP_WRAPPER_NAME]: {
+          name: COMPONENT_TOOLTIP_WRAPPER_NAME,
+          template: '<slot />',
+        },
+      },
+    },
+    slots: {
+      default: options?.slotContent ?? 'Stubbed slot content',
+    },
+  });
+}