[PM-25330] Fix B64 type (#417)

## 🎟️ Tracking

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point to where this change is coming from. -->
https://bitwarden.atlassian.net/browse/PM-25330

## 📔 Objective

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you're fixing or new feature you're adding. -->

Currently `bitwarden_wasm_internal.d.ts` produces: 
```
export type B64 = String;
```

This PR makes it produce:

```
export type B64 = string;
```

In TypeScript the `string` primitive is case sensitive. This was causing
breaking changes to TS clients.

## ⏰ Reminders before review

- Contributor guidelines followed
- All formatters and local linters executed and passed
- Written new unit and / or integration tests where applicable
- Protected functional changes with optionality (feature flags)
- Used internationalization (i18n) for all UI strings
- CI builds passed
- Communicated to DevOps any deployment requirements
- Updated any necessary documentation (Confluence, contributing docs) or
informed the documentation
  team

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Author: Thomas-Avery

crates/bitwarden-encoding/src/b64.rs

@@ -16,7 +16,7 @@ use crate::FromStrVisitor;
 #[serde(into = "String")]
 #[derive(Tsify)]
 #[tsify(into_wasm_abi, from_wasm_abi)]
-pub struct B64(#[tsify(type = "String")] Vec<u8>);
+pub struct B64(#[tsify(type = "string")] Vec<u8>);
 
 /// Base64 encoded data
 ///