Ensure that the correct default currency symbols are used for fees on the view quote screen

[danjm]

This PR fixes an issues found by @tmashuang while reviewing v9.3.0

It ensures that fees on the view quote screen - in both the fees card and in the gas modal - use the correct currency symbol. On mainnet this will be ETH. On custom networks, this will be the currency symbol set by the user, or if no currency symbol has been set, it will be the symbol of the default token for that network.

Demo video is here: https://www.veed.io/download/a2f4f25e-f0b6-4658-8909-4f48730f1890

[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 [42d2ece]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• build viz: Build System
• code coverage: Report
• storybook: Storybook
• all artifacts

Page Load Metrics (617 ± 45 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	44	87	56	10	5
		domContentLoaded	352	830	615	94	45
		load	353	831	617	94	45
		domInteractive	352	830	615	94	45

[brad-decker]

LGTM.