Removed the remote XCRemoteSwiftPackageReference and pointed
MarkdownEngine/MarkdownEngineCodeBlocks/MarkdownEngineLatex at the
XCLocalSwiftPackageReference for Vendor/swift-markdown-engine instead.
Package.resolved drops the now-irrelevant remote pin (HighlighterSwift
and SwiftMath stay remote, only swift-markdown-engine itself moved
local).
Also bumps the submodule pointer to include three warning fixes made
directly in the vendored source (var->let, unused local, #selector) —
first real edits to the package now that it's locally editable.
Puranjay Savar Mattas
226d6fb748