feat(snaps): Add loading variant to Snap UI button

[david0xd]

Description

This PR enables loading button variant for Snaps UI.

Notes

• Targets Snaps release integration PR: chore: Bump Snaps packages #29275

Related issues

Fixes: MetaMask/snaps#2694

Related PR dependencies

Snaps monorepo: MetaMask/snaps#2930

Manual testing steps

1. Create some example Snap for testing and add Snap UI Button with loading variant.
   Example:

<Button loading={true} variant="primary">
    Example Button
</Button>
<Button loading={true} variant="destructive">
    Example Button
</Button>

Screenshots/Recordings

Before

Loading button variant was not available before.

After

Screen.Recording.2024-12-09.at.16.26.44.mov

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[metamaskbot]

Builds ready [346d6c6]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (MMI): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6
  • common: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • offscreen: 0
  • ui: 0, 1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1994 ± 83 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	300	2393	1766	631	303
		domContentLoaded	1646	2386	1967	168	81
		load	1682	2394	1994	172	83
		domInteractive	25	56	32	8	4
		backgroundConnect	8	89	29	23	11
		firstReactRender	16	93	27	20	10
		getState	84	297	152	57	27
		initialActions	0	1	0	0	0
		loadScripts	1200	1958	1509	169	81
		setupStore	7	77	13	15	7
		uiStartup	1936	2856	2351	231	111

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 151 Bytes (0.00%)
• common: 0 Bytes (0.00%)