[NFC][cling] Use StringRef::{starts,ends}_with

[devajithvs]

Follows the changes introduced in https://reviews.llvm.org/D136030 to be more compatible with std::string and std::string_view.

This Pull request:

Changes or fixes:

Checklist:

• [x] tested changes locally
• [ ] updated the docs (if necessary)

This PR fixes #

[github-actions[bot]]

Test Results

    12 files      12 suites   2d 1h 30m 41s :stopwatch:  2 563 tests  2 560 :white_check_mark:   0 :zzz: 3 :x: 28 834 runs  28 693 :white_check_mark: 137 :zzz: 4 :x:

For more details on these failures, see this check.

Results for commit 5a8e4136.