Move JuliaSyntax + JuliaLowering into the main tree (#59870)

There's been some interest in having the new Julia compiler frontend
(JuliaSyntax + JuliaLowering) in the main Julia tree so that these are
easier to work on together and so the new lowering code can co-evolve
with changes to Core more easily.

Author: topolarity

JuliaLowering/.gitignore

@@ -0,0 +1 @@
+/Manifest.toml

JuliaLowering/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2024 JuliaHub and contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

JuliaLowering/Project.toml

@@ -0,0 +1,22 @@
+name = "JuliaLowering"
+uuid = "f3c80556-a63f-4383-b822-37d64f81a311"
+authors = ["Claire Foster <[email protected]> and contributors"]
+version = "1.0.0-DEV"
+
+[deps]
+JuliaSyntax = "70703baa-626e-46a2-a12c-08ffd08c73b4"
+
+[sources]
+JuliaSyntax = {path = "../JuliaSyntax"}
+
+[compat]
+julia = "1"
+
+[extras]
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+Markdown = "d6f4376e-aef5-505a-96c1-9c027394607a"
+FileWatching = "7b1f6079-737a-58dc-b8bc-7a2ca5c1b5ee"
+REPL = "3fa0cd96-eef1-5676-8a61-b3b8758bbffb"
+
+[targets]
+test = ["Test", "FileWatching", "Markdown", "REPL"]