Move chplcheck into its own directory in tools and have both proj…

…ects use an `src` folder (chapel-lang#23817)

The new structure is as follows:

```
chapel-py
├── README.md
├── examples
│   ├── gather_unstable.py
│   └── replace.py
├── setup.py
└── src
    ├── chapel
    │   ├── __init__.py
    │   └── replace
    │       └── __init__.py
    ├── chapel.cpp
    └── method-tables.h

chplcheck
├── chplcheck
└── src
    ├── chplcheck.py
    ├── driver.py
    ├── lsp.py
    └── rules.py
```

This way, we have two advantages:

1. `chplcheck`, being a separate project, is in its own folder, can have
its own README and top-level files.
2. Because of `src`, we can have a `chplcheck` file in the root
directory, even if eventually we do write `chplcheck` as a module.

Reviewed by @jabraham17 -- thanks!

tools/chapel-py/setup.py

@@ -47,6 +47,7 @@
 
 setup(name = "chapel",
       version = "0.1",
+      package_dir = {'': 'src'},
       packages = ['chapel', 'chapel.replace'],
-      ext_modules = [Extension("chapel.core", ["chapel.cpp"], extra_compile_args = CXXFLAGS, extra_link_args=LDFLAGS)]
+      ext_modules = [Extension("chapel.core", ["src/chapel.cpp"], extra_compile_args = CXXFLAGS, extra_link_args=LDFLAGS)]
       )

tools/chapel-py/runChplcheck → tools/chplcheck/chplcheck

@@ -26,5 +26,5 @@ if [ -z "$CHPL_HOME" ]; then
 fi
 
 exec $CHPL_HOME/util/config/run-in-venv-with-python-bindings.bash \
-     $CHPL_HOME/tools/chapel-py/chplcheck/__init__.py "$@"
+     $CHPL_HOME/tools/chplcheck/src/chplcheck.py "$@"