[orc-rt] Add ConnectionSpec, a connection-string parser (#225304)
Parses the string a process is given to describe the connection it
should establish with its peer:
<transport>[:<action>]=<descriptor>
Checking is punctuation only: the transport and action are opaque tokens
and the descriptor's syntax belongs to the transport, so a spec parses
without knowing which transports this process was built with.
The grammar is LLVM's (#225075), so the same vocabulary reaches an
orc-rt executor and an LLVM controller. A registry mapping transports to
the connectors that implement them will be added in a follow-up commit.
llvm-project
9c096068 - [orc-rt] Add ConnectionSpec, a connection-string parser (#225304)
