[BugFix] Fix backup failure due to case-sensitive table name conflict

[saahilbarai]

Why I'm doing:

Cherry picking bug fix from main StarRocks branch into the pinterest 3.3 branch.

I am making this change due to fix an issue where two table names with the same name but differing case throws a semantic error citing duplicated tables for the backup process.

What I'm doing:

Amending the usage of a case insensitive tree map used to process both the backup and restore process in favor of a case sensitive tree map.

Fixes #issue
StarRocks#50949

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.3
  • 3.2
  • 3.1
  • 3.0
  • 2.5