Remove special-casing for editable requirements (#3869)

## Summary

There are a few behavior changes in here:

- We now enforce `--require-hashes` for editables, like pip. So if you
use `--require-hashes` with an editable requirement, we'll reject it. I
could change this if it seems off.
- We now treat source tree requirements, editable or not (e.g., both `-e
./black` and `./black`) as if `--refresh` is always enabled. This
doesn't mean that we _always_ rebuild them; but if you pass
`--reinstall`, then yes, we always rebuild them. I think this is an
improvement and is close to how editables work today.

Closes #3844.

Closes #2695.

scripts/packages/dependent_editables/first_editable/.gitignore

@@ -1,2 +0,0 @@
-# Artifacts from the build process.
-*.egg-info/

scripts/packages/dependent_editables/first_editable/setup.py

@@ -1,3 +0,0 @@
-from setuptools import setup
-
-setup(name="first-editable", version="0.0.1", install_requires=[])

scripts/packages/dependent_editables/second_editable/.gitignore

@@ -1,3 +0,0 @@
-# Artifacts from the build process.
-*.egg-info/
-build/

scripts/packages/dependent_editables/second_editable/setup.py

@@ -1,9 +0,0 @@
-from setuptools import setup
-
-setup(
-    name="second-editable",
-    version="0.0.1",
-    install_requires=[
-        "first-editable",
-    ],
-)