Restore UI tests on Julia 1.10 through nightly

[KristofferC]

Summary

• raise the minimum Julia version to 1.10, bump Debugger to 0.8.0, and allow JuliaInterpreter 0.11
• repair Julia 1.12 REPL state, terminal color propagation, and next-expression rendering
• update the Highlights 0.6 UI snapshots and run rendering snapshots only on the stable Julia lane
• test Julia 1.10, 1.11, stable, and nightly across all existing operating systems
• use the TerminalRegressionTests support branch through both [sources] and an explicit cross-version CI pin
• remove obsolete highlighting compatibility constants and clean up documentation typos

Dependency

Depends on JuliaDebug/TerminalRegressionTests.jl#24. The branch pin is intentional until TerminalRegressionTests 0.3.0 is reviewed and released.

Local verification

• Julia 1.10.11: full non-UI suite
• Julia 1.11.9: full non-UI suite
• Julia 1.12.6: full suite including all UI snapshots
• Julia 1.14.0-DEV.2617: full non-UI suite
• Julia 1.10 REPL modal-state API surface checked directly