docs: split types from syntax (#11013)

move together all syntactic and semantic information into one
page, and add a page on data types, which in turn links to the syntax and
semantics.

also split out the note on scoping rules into its own page.

Co-authored-by: Ryan Hendrickson <ryan.hendrickson@alum.mit.edu>

doc/manual/src/language/scope.md

@@ -0,0 +1,14 @@
+# Scoping rules
+
+Nix is [statically scoped](https://en.wikipedia.org/wiki/Scope_(computer_science)#Lexical_scope), but with multiple scopes and shadowing rules.
+
+* primary scope: explicitly-bound variables
+  * [`let`](./syntax.md#let-expressions)
+  * [`inherit`](./syntax.md#inheriting-attributes)
+  * [function](./syntax.md#functions) arguments
+
+* secondary scope: implicitly-bound variables
+  * [`with`](./syntax.md#with-expressions)
+
+Primary scope takes precedence over secondary scope.
+See [`with`](./syntax.md#with-expressions) for a detailed example.