[LLDB] Fix parsing of IPv6 host:port inside brackets

Summary:
When using IPv6 host:port pairs, typically the host is put inside
brackets, such as [2601:1234:...:0213]:5555, and the UriParser
can handle this format.

However, the Android infrastructure in LLDB assumes an additional
brackets around the host:port pair, such that the entire host:port
string can be treated as the host (which is used as an Android Serial
Number), and UriParser cannot handle multiple brackets. Parsing
inputs with such extra backets requires searching the closing bracket
from the right.

Test: BracketedHostnameWithPortIPv6 covers the case mentioned above

Reviewers: #lldb, labath

Reviewed By: labath

Subscribers: kwk, shafik, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D76736