Properly delegate calls to original DebugProbes when installing a debugger

[qwwdfsad]

Currently, kotlinx-coroutines-debug unconditionally overwrites any previously installed debug probes, which may lead to various conflicts when more than one agent with DebugProbes support is installed.

The issue was discovered when proposing an internal design for Deft tracer, so it's likely to be the issue in the future, though there is no urgency to fix that right now

[dovchinnikov]

Alternatively, support ServiceLoader-based solution in kotlin-stdlib; this would enable custom implementations which are compatible with JPMS and not require VM agent capability