[ABNF] Add a rule for function calls. (#1747)

* [ABNF] Add a rule for function calls.

This does not change the language. It just slightly reformulates the grammar for
greater clarity and to help establish a nomenclature for constructs.

Also remove a trailing space.

* [ABNF] Re-generate markdown.

Co-authored-by: collin <16715212+collinc97@users.noreply.github.com>

docs/grammar/abnf-grammar.txt

@@ -161,7 +161,7 @@ string-literal-element = not-double-quote-or-backslash
                        / unicode-character-escape
 
 integer-literal = unsigned-literal
-                / signed-literal 
+                / signed-literal
 
 atomic-literal = integer-literal
                / field-literal
@@ -228,7 +228,9 @@ group-literal = product-group-literal / affine-group-literal
 primary-expression = identifier
                    / literal
                    / "(" expression ")"
-                   / identifier function-arguments
+                   / function-call
+
+function-call = identifier function-arguments
 
 function-arguments = "(" [ expression *( "," expression ) [ "," ] ] ")"