[V3] Encode Pending Browser Switch Request as Base64 String

[sshropshire]

Summary of changes

• Rename BrowserSwitchPendingRequest to BrowserSwitchStartResult
• Support ComponentActivity for BrowserSwitchClient#start() method
• Rename BrowserSwitchResult to BrowserSwitchParseResult
• Remove BrowserSwitchInfo helper class

Checklist

• [x] Added a changelog entry

Authors

List GitHub usernames for everyone who contributed to this pull request.

• @sshropshire