doc: Consistently spell case-insensitive

While almost all occurrences of "case-insensitive{ly}" were spelled with
a dash, a few were using "case insensitive{ly}" with a space instead. Fix
by changing these to use a dash to be consistent.

Discussion: https://postgr.es/m/7657EDEE-5EE2-4AAB-BA95-47B4F71653E1@yesql.se

doc/src/sgml/func.sgml

@@ -5604,7 +5604,7 @@ substring('foobar' similar '#"o_b#"%' escape '#')    <lineannotation>NULL</linea
         <returnvalue>boolean</returnvalue>
        </para>
        <para>
-        String matches regular expression, case insensitively
+        String matches regular expression, case-insensitively
        </para>
        <para>
         <literal>'thomas' ~* 'T.*ma'</literal>
@@ -5632,7 +5632,7 @@ substring('foobar' similar '#"o_b#"%' escape '#')    <lineannotation>NULL</linea
         <returnvalue>boolean</returnvalue>
        </para>
        <para>
-        String does not match regular expression, case insensitively
+        String does not match regular expression, case-insensitively
        </para>
        <para>
         <literal>'thomas' !~* 'T.*ma'</literal>

doc/src/sgml/query.sgml

@@ -134,7 +134,7 @@ CREATE TABLE weather (
     differently than above, or even all on one line.  Two dashes
     (<quote><literal>--</literal></quote>) introduce comments.
     Whatever follows them is ignored up to the end of the line.  SQL
-    is case insensitive about key words and identifiers, except
+    is case-insensitive about key words and identifiers, except
     when identifiers are double-quoted to preserve the case (not done
     above).
    </para>

doc/src/sgml/syntax.sgml

@@ -144,7 +144,7 @@ INSERT INTO MY_TABLE VALUES (3, 'hi there');
      <primary>case sensitivity</primary>
      <secondary>of SQL commands</secondary>
     </indexterm>
-    Key words and unquoted identifiers are case insensitive.  Therefore:
+    Key words and unquoted identifiers are case-insensitive.  Therefore:
 <programlisting>
 UPDATE MY_TABLE SET A = 5;
 </programlisting>