This is the start of the removal of the C++ implementation of libSyntax
in favor of the new Swift Parser and Swift Syntax libraries. Now that
the Swift Parser has switched the SwiftSyntaxParser library over to
being a thin wrapper around the Swift Parser, there is no longer any
reason we need to retain any libSyntax infrastructure in the swift
compiler.
As a first step, delete the infrastructure that builds
lib_InternalSwiftSyntaxParser and convert any scripts that mention
it to instead mention the static mirror libraries. The --swiftsyntax
build-script flag has been retained and will now just execute the
SwiftSyntax and Swift Parser builds with the just-built tools.
The utils/dev-scripts/at-to-filelist, utils/dev-scripts/split-cmdline and utils/build-parser-lib scripts needed to be reformatted with the black tool to agree with the linter.
