Identified with misc-include-cleaner.

This keeps common operations together, and should make it easier to write
re-usable dylib managers in the future (e.g. a DylibManager that uses
the EPC's remote-execution APIs to implement load and lookup).

This migrates the dylib manager lookup and related APIs to replace
ExecutorAddress with ExecutorSymbolDef so that in the future we can
model JITSymbolFlags for these symbols. The current change should be NFC
as we are only setting the Exported symbol flag.

Configure the plugin to automatically call the debugger rendezvous breakpoint `__jit_debug_register_code()` for every translation unit (enabled) or never at all (disabled). Default API and behavior remain unchanged.

If AutoRegisterCode is turned off, it's the client's own responsibility to call the rendezvous breakpoint function at an appropriate time.
Depending on the complexity of the debugger's rendezvous breakpoint implementation, this can provide significant performance improvements in cases where many debug objects are added in sequence.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D147310

Most ORC APIs work with ExecutorAddr by default since 8b1771bd9f3, so we don't
need to wrap these values in ExecutorAddr(...) calls any more.

Similar to the EPCEHFrameRegistrar change in c977251ef6f, this allows clients
who have sourced a dylib handle via a side-channel to search that dylib to
find the registration functions.

This patch defaults to the existing behavior in the case where the client does
not specify a handle to use.

The directive pollutes the namespace of all files which include the
header.

Use alternate ways to reference the namespace constituents instead.

Adds explicit narrowing casts to JITLinkMemoryManager.cpp.

Honors -slab-address option in llvm-jitlink.cpp, which was accidentally
dropped in the refactor.

This effectively reverts commit 6641d29b70993bce6dbd7e0e0f1040753d38842f.

This reverts commit e50aea58d59c8cfae807a7fee21c4227472c0678 while I
investigate bot failures.