UX: Multichain: Use contants for AssetListConversionButton variants

[darkwing]

Description

Since we're expecting one of three strings for the variant of AssetListConversionButton, we should make those keys a constant to be imported and used.

Manual testing steps

No functional change.

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[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (313abb1) 68.68% compared to head (6a92640) 68.69%.
Report is 6 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #21333   +/-   ##
========================================
  Coverage    68.68%   68.69%           
========================================
  Files         1019     1019           
  Lines        40878    40879    +1     
  Branches     10917    10917           
========================================
+ Hits         28077    28078    +1     
  Misses       12801    12801           

Files	Coverage Δ
ui/components/app/asset-list/asset-list.js	72.88% <ø> (ø)
ui/components/app/nfts-tab/nfts-tab.js	88.24% <ø> (ø)
...-conversion-button/asset-list-conversion-button.js	100.00% <100.00%> (ø)

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[metamaskbot]

Builds ready [a44b569]

• 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
  • common: 0, 1, 2, 3, 4, 5, 6
  • content-script: 0
  • contentscript: contentscript
  • disable-console: disable-console
  • inpage: inpage
  • policy-load: policy-load
  • sentry-install: sentry-install
  • ui: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1243 ± 362 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	90	170	118	24	12
		domContentLoaded	72	167	108	28	14
		load	85	2059	1243	753	362
		domInteractive	72	167	108	28	14

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 688 Bytes (0.01%)
• common: 0 Bytes (0.00%)

[metamaskbot]

Builds ready [6a92640]

• 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
  • common: 0, 1, 2, 3, 4, 5, 6
  • content-script: 0
  • contentscript: contentscript
  • disable-console: disable-console
  • inpage: inpage
  • policy-load: policy-load
  • sentry-install: sentry-install
  • ui: 0, 1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1289 ± 335 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	82	139	100	14	7
		domContentLoaded	70	137	95	18	9
		load	82	1859	1289	697	335
		domInteractive	70	137	95	18	9

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 681 Bytes (0.01%)
• common: 0 Bytes (0.00%)