_table-row_: Performance fix: place table in const/text() instead of const/@values

This is an interesting one.

For some context: TAME uses `csvm` files to provide syntactic sugar for
large tables of values ("rate tables", as they're often called, since they
contain insurance rates and other data).  This gets desugared into a `csv`
which in turn is compiled via `csv2xml` into a package.  That package uses
the `_table-*_` templates to define a table, which is represented as a
matrix using `const/@values`.

Here's an example of a generated table in a package:

```
  <t:create-table name="foo">
        <t:table-rows data="
          1,2,3;
          4,5,6;" />
  </t:create-table>
```

Some of the tables are quite large, generating tens of MiB of data in
`@data`.  This in itself isn't a problem.  But when Saxon parses the `@data`
attribute, it normalizes the whitespace, as mandated by the XML spec, and
removes the newlines.  Therefore, when the template is expanded and the
`xmlo` file is produced, the template produced a `const/@values` with a huge
amount of data on one line.

Then, when another package imports that `xmlo` file via `<import
package="..." />`, which is done via `document()` in XSLT, Saxon takes a
long time to parse it.  60s on my machine for a ~20MiB line.

This problem does not exist for JS fragments; Saxon doesn't mind large text
nodes.  So that is the approach that is taken here.

The template system doesn't have a way to output text yet, so this takes an
approach that minimizes changes as much as possible:

  - `param-copy` will expand `with-param/@value` as a text node.
  - `const/@values="-"` will cause TAME to use the child text node as the
    value of `@values`.
  - `_table-rows_` is modified to use the above two features.

The reason for using `@values="-"` is so that other parts of the compiler do
not have to be modified to recognize the new text convention, which is
otherwise awkward because newlines are text nodes.  The `-` convention comes
from command line programs, which means "read from stdin", generally; this
is okay since `-` is never a valid matrix specification.

This must have been a problem for a very long time, but wasn't all that
noticeable until recent performance optimizations, since so many other things
around it were also slow.

DEV-15131

core/vector/table.xml

@@ -160,7 +160,11 @@
       <const name="{@__tid@}_RATE_TABLE"
              type="float"
              desc="{@__tname@} table; {@__desc@}"
-             values="@data@" />
+             values="-">
+        <!-- `@values="-"` above tells TAME to read the value from the
+             child text node -->
+        <param-copy name="@data@" />
+      </const>
     </if>
     <unless name="@data@">
       <const name="{@__tid@}_RATE_TABLE"

src/current/compiler/js.xsl

@@ -472,7 +472,7 @@
   <param name="const" as="element( lv:const )" />
 
   <variable name="values-def" as="xs:string?"
-            select="$const/@values" />
+            select="compiler:const-values( $const )" />
 
   <choose>
     <when test="$values-def and contains( $values-def, ';' )">
@@ -487,6 +487,21 @@
 </function>
 
 
+<function name="compiler:const-values" as="xs:string?">
+  <param name="const" as="element( lv:const )" />
+
+  <!-- @values="-", a convention from command-line programs where '-' means
+       "read from stdin", will take the value from the child text of the
+       constant; this is done because Saxon performs very, very poorly on
+       huge single-line attributes (e.g. 60s for ~20MiB single-line
+       attribute) -->
+  <sequence select="if ( $const/@values = '-' ) then
+                        $const/text()
+                      else
+                        $const/@values" />
+</function>
+
+
 <!--
   Produce a sequence of items
 
@@ -505,7 +520,9 @@
 
     <when test="$set/@values and $allow-values">
       <sequence select="tokenize(
-                          normalize-space( $set/@values ), ',' )" />
+                          normalize-space(
+                            compiler:const-values( $set ) ),
+                          ',' )" />
     </when>
 
     <otherwise>

src/current/include/preproc/template.xsl

@@ -653,11 +653,13 @@
   <variable name="varname" select="@name" />
   <variable name="param" select="$params[ @name=$varname ]" />
 
-  <variable name="copy" as="node()*">
+  <variable name="copy">
     <choose>
-      <!-- TAMER desugared @values@ application convention (see tplshort.rs) -->
-      <when test="$param/@value">
-        <!-- the value is the name of a template to copy the body from -->
+      <!-- TAMER desugared @values@ application convention (see
+           tplshort.rs); this will go away once the template system is fully
+           implemented in TAMER -->
+      <when test="$varname = '@values@' and $param/@value">
+        <!-- the value may be the name of a template to copy the body from -->
         <variable name="dsgr" select="$param/@value" />
 
         <!-- the template is always positioned as the immeditely-following
@@ -667,6 +669,11 @@
                               /*" />
       </when>
 
+      <!-- non-node value is copied as text -->
+      <when test="$param/@value">
+         <sequence select="string( $param/@value )" />
+      </when>
+
       <!-- old applicatication convention has child nodes within
            `with-param` -->
       <otherwise>