fix (cherry-pick): 0 token balance in send flow (#28136)

[danjm]

Cherry-picks #28136 (1fd9510). Original PR description:

Description

Fixes an issue where token balance showed as 0 during send flow. This occurred when clicking the token in the token list, then clicking the send button from the token details page.

When going send first and then picking a token, picking decimals was a number:

But when going token first and then clicking send , decimals was a string and skipped calculating the balance.

calcTokenAmount seems to work with either string or number, so changing logic from
#27083 which introduced the number check

Related issues

Fixes: #28112

Manual testing steps

1. Click on an erc20 token on the token list
2. Click the send button on the token details page
3. Choose a destination account
4. The balance under the asset picker should be accurate

Screenshots/Recordings

Before

After

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  Standards.
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Description

Related issues

Fixes:

Manual testing steps

1. Go to this page...

Screenshots/Recordings

Before

After

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]

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[metamaskbot]

Builds ready [13a3537]

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Page Load Metrics (1930 ± 125 ms)

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		domContentLoaded	1526	2385	1903	257	124
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