[Android] Update "Open tabs in Custom Tabs" setting copy

[timchilds]

Description

Update the copy for the Open tabs in Custom Tabs settings toggle:

Header: Open external links in Brave webview
Description: Opens links from other apps in a Brave webview. Note: Brave must be set as your default browser.

Why

The existing copy does not accurately describe what happens when the setting is enabled.

cc @bradleyrichter @anthonypkeane @SergeyZhukovsky @samartnik @rmcfadden3

[hffvld]

Verified on Pixel 7 using version(s):

Device/OS: Pixel 7 [panther_beta-user 14 UPB2.230407.019 release-keys]
Brave build: 1.53.83
Chromium: 114.0.5735.110 (Official Build) beta (64-bit)
Revision: 1c828682b85bbc70230a48f5e345489ec447373e-refs/branch-heads/5735_90@{#13}

NOTE: Confirmed with @deeppandya that the title string updated from Open external links in Brave webview to Open external links in Brave.

Filed follow-up issue #30947

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STEPS:

1. Launch Brave
2. Three-dot Menu > Settings
3. Scroll down and find Open external links in Brave > Verify

ACTUAL RESULTS:

• Verified that the title is Open external links in Brave
• Verified that subtitle is Opens link from other apps in a Brave webview. Note: Brave must be set as your default browser.
• Verified that the default setting is ON
• Verified that links are opened as expected depending on the setting ON or OFF

timestamp_12-49-48_12-51-00.mp4