* Move collapse(expansions:for:attachedTo:) to SwiftSyntaxMacroExpansion
* SwiftSyntaxMacroExpansion.expandAttachedMacro() now perform collapsing
* SwiftSyntaxMacroExpansion.expandAttachedMacroWithoutCollapsing()
to keep old behavior
* IPC request 'getCapability' now sends the host protocol version
* Unified IPC response 'macroExpansionResult' that returns single string
for both 'expandFreestandingMacro' and 'expandAttachedMacro'
* Compiler accepts old 'expandFreestandingMacroResult' and
'expandAttachedMacroResult' to keep compatibility
* Plugins check the compiler's protcol version to see if it suppports
'macroExpansionResult', and fall back to old behavior if necessary
The compiler knows (from a macro declaration) what freestanding macro
role a macro implementation is expected to implement. Pass that through
to the macro expansion code itself, rather than guessing based on the
protocol conformances of the implementation type. We already use this
approach with attached macros, so this is more of the same.
Eliminates a crash and improves diagnostics when the freestanding macro
role and its implementation are out of sync, fixing rdar://110418969.
The macro tests were all using "REQUIRES: OS=macosx" as a proxy for
"have the Swift Swift parser". There was an existing feature for this,
but it was just checking whether the path was passed through. Fix that
to use the same variable as in CMake.
Also remove all extraneous `-I` and `-L` to the host libs in the target
invocations.
