Mention "no preceding space" rule for left paren in function declaration and lambda expressions

[muzimuzhi]

Currently this rule is mentioned in

• ‹app-args› in sec. 2.1.11.4 Application Expressions

  Note that there is no space allowed before the opening parenthesis of the application.
  https://pyret.org/docs/latest/Expressions.html#%28part._s~3aapp-expr%29

• ‹inst-expr› in sec. 2.1.11.7 Instantiation Expressions

  Spaces are not permitted before the left-angle bracket or after the right-angle bracket
  https://pyret.org/docs/latest/Expressions.html#%28part._s~3ainst-expr%29

But Pyret will also complain if a space exists before opening parenthesis in

• function declaration expressions like fun f (n): n end
  https://pyret.org/docs/latest/s_declarations.html#%28part._s~3afun-decl%29
• lambda expressions lam (n): n end
  https://pyret.org/docs/latest/Expressions.html#%28part._s~3alam-expr%29

This also seems to suggest, that the grammar rule for ‹args› (line 916 below)

pyret-docs/src/lang/forms.scrbl

Lines 911 to 916 in e54e933

	fun-decl: FUN NAME fun-header [BLOCK] COLON doc-string block where-clause END
	fun-header: ty-params args return-ann
	ty-params:
	[LANGLE list-ty-param* NAME RANGLE]
	list-ty-param: NAME COMMA
	args: LPAREN [list-arg-elt* binding] RPAREN

should be updated to

args: PARENNOSPACE [list-arg-elt* binding] RPAREN

As a reference, in pyret-grammar.bnf in pyret-lang repo, ‹args› has grammar rule

args: (PARENNOSPACE|PARENAFTERBRACE) [binding (COMMA binding)*] RPAREN