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/command-ref/env-common.md

@@ -10,7 +10,7 @@ Most Nix commands interpret the following environment variables:
 - <span id="env-NIX_PATH">[`NIX_PATH`](#env-NIX_PATH)</span>
 
   A colon-separated list of directories used to look up the location of Nix
-  expressions using [paths](@docroot@/language/values.md#type-path)
+  expressions using [paths](@docroot@/language/types.md#type-path)
   enclosed in angle brackets (i.e., `<path>`),
   e.g. `/home/eelco/Dev:/etc/nixos`. It can be extended using the
   [`-I` option](@docroot@/command-ref/opt-common.md#opt-I).

doc/manual/src/command-ref/nix-env/install.md

@@ -57,7 +57,7 @@ The arguments *args* map to store paths in a number of possible ways:
   easy way to copy user environment elements from one profile to
   another.
 
-- If `--from-expression` is given, *args* are [Nix language functions](@docroot@/language/constructs.md#functions) that are called with the [default Nix expression] as their single argument.
+- If `--from-expression` is given, *args* are [Nix language functions](@docroot@/language/syntax.md#functions) that are called with the [default Nix expression] as their single argument.
   The derivations returned by those function calls are installed.
   This allows derivations to be specified in an unambiguous way, which is necessary if there are multiple derivations with the same name.
 

doc/manual/src/command-ref/opt-common.md

@@ -143,7 +143,7 @@ Most Nix commands accept the following command-line options:
 
   This option is accepted by `nix-env`, `nix-instantiate`, `nix-shell` and `nix-build`.
   When evaluating Nix expressions, the expression evaluator will automatically try to call functions that it encounters.
-  It can automatically call functions for which every argument has a [default value](@docroot@/language/constructs.md#functions) (e.g., `{ argName ?  defaultValue }: ...`).
+  It can automatically call functions for which every argument has a [default value](@docroot@/language/syntax.md#functions) (e.g., `{ argName ?  defaultValue }: ...`).
 
   With `--arg`, you can also call functions that have arguments without a default value (or override a default value).
   That is, if the evaluator encounters a function with an argument named *name*, it will call it with value *value*.