Index everything on unicode_texas page

Resolves issue #1373.

This means that from now on some things may appear more than once in
the search. We'll see how annoying it is. If it is, we can start
removing symbols that are explained elsewhere (but note that a lot of
things are only mentioned on unicode_texas page, so don't revert the
whole commit).

doc/Language/unicode_texas.pod6

@@ -50,6 +50,7 @@ line), or C<Zp> (Separator, paragraph) property.
 This list contains the single codepoints [and their Texas (ASCII)
 equivalents] that have a special meaning in Perl 6.
 
+X<|«>X<|»>X<|×>X<|÷>X<|≤>X<|≥>X<|≠>X<|−>X<|∘>X<|≅>X<|π>X<|τ>X<|𝑒>X<|∞>X<|…>X<|‘>X<|’>X<|‚>X<|“>X<|”>X<|„>X<|｢>X<|｣>X<|⁺>X<|⁻>X<|¯>X<|⁰>X<|¹>X<|²>X<|³>X<|⁴>X<|⁵>X<|⁶>X<|⁷>X<|⁸>X<|⁹>X<|∅>X<|∈>X<|∉>X<|∋>X<|∌>X<|⊆>X<|⊈>X<|⊂>X<|⊄>X<|⊇>X<|⊉>X<|⊃>X<|⊅>X<|≼>X<|≽>X<|∪>X<|∩>X<|∖>X<|⊖>X<|⊍>X<|⊎>
 =table
   Symbol | Codepoint | Texas      | Remarks
   =======|===========|============|=========================
@@ -122,6 +123,7 @@ Texas equivalents are ordinary subroutines, not operators:
 
 The Texas alternatives are as follows:
 
+X<|⚛=>X<|⚛>X<|⚛+=>X<|⚛-=>X<|⚛−=>X<|++⚛>X<|⚛++>X<|--⚛>X<|⚛-->
 =table
   Symbol | Texas            | Remarks
   ===============================================================
@@ -142,6 +144,7 @@ composition for their Texas (ASCII) equivalents.  Note the codepoints
 are shown space-separated but should be entered as adjacent codepoints
 when used.
 
+X<|»=»>X<|«=«>X<|«=»>X<|»=«>
 =table
   Symbol | Codepoints       | Texas   | Since | Remarks
   =======|==================|=========|=======|=========================