Remove some conditionals used for regex literals (#17)

Relates to #16 / cc
@slevithan

The conditional negative lookaheads were conditional based on absence of
`#` in the opening delimiter. This can be simplified by including `/` in
the negative lookaheads and moving them before the opening delimiter.

(The comment rule seems like it is not actually necessary since
`#comment` is given a higher priority, but I kept it for good measure.)

Swift.tmLanguage.yaml

@@ -1824,9 +1824,9 @@ repository:
       - name: string.regexp.line.swift
         match: |-
           (?x)
+          (?!/\s)         # non-extended regex literals may not start with a space or tab
+          (?!//)          # disambiguation with line comments (redundant since comment rules occur earlier)
           (((\#+)?)/)     # (1) for captures, (2) for matching end, (3) for conditionals
-          (?(3)|(?!/))   # is not a comment
-          (?(3)|(?!\s))  # does not start with a space or tab
           (\\\s)? # (4) may start with an escaped space or tab
           (?<guts>
             (?>   # no backtracking, avoids issues with negative lookbehind at end

grammar-test.swift

@@ -553,6 +553,7 @@ let r = /\Q/1/ //x
 let r = /\ \Q/1/ //x
 let r = #/\Q/1/# //x
 let r = ##/\Q/1/# /## //x
+let quote = /\Q/\E/  // FIXME? xcode doesn't handle this either?
 let nested = /\Q^[xy])+$\E/ // FIXME: xcode does not parse this as a regex because of the `)` (??)
 let nested = /[a\Q]\E]/
 let nested = /ab[^a^~~b--c&&d\Qa\E\f] [\w--\d] foo [:a] foo [:a:] [-a-] [a-c-d]/
@@ -770,6 +771,10 @@ let r = ^^(/x/)
 
 
 //// A regex literal may not start or end with a space or tab.
+let initialSpace = / x/
+let finalSpace = /x /
+let initialSpace = #/ x/#
+let finalSpace = #/x /#
 
 // Unapplied '/' in a call to 'reduce':
 let x = array.reduce(1, /) / 5