Overhaul IsPlistMatrixRep and IsPlistVectorRep

- change `IsPlistMatrixRep` to *not* be a row list type; so instead
  of storing a list of `IsPlistVectorRep` instances, they now store an
  old-style matrix in `IsMatrix and IsPlistRep`. This in turn allows
  to simplify and optimize a lot of code, e.g. matrix arithmetic can
  now just dispatch to that for plain lists.
- use `BindConstant` on `BDPOS` etc. for best performance
- set `IsNoImmediateMethodsObject` filter for both for better performance
- rename `EMPOS` and `RLPOS` to `NUM_ROWS_POS` and `NUM_COLS_POS`
- allow semirings as basedomain
- fix various vector/matrix constructors to copy their inputs lists
  instead of reusing them inside (that can lead to bad bugs)
- removed a bunch of (now) redundant methods that didn't seem to
  provide any benefits (such as improved performance)
- ...

lib/matobjplist.gd

@@ -29,7 +29,7 @@
 ##  in a row list matrix
 ##  (see Section <Ref Subsect="Operations for Row List Matrix Objects"/>).
 ##  It is internally represented as a positional object
-##  (see <Ref Filt="IsPositionalObjectRep"/> that stores 2 entries:
+##  (see <Ref Filt="IsPositionalObjectRep"/> that stores two entries:
 ##  <Enum>
 ##  <Item>
 ##    its base domain
@@ -45,7 +45,7 @@
 ##  <#/GAPDoc>
 ##
 DeclareRepresentation( "IsPlistVectorRep",
-   IsVectorObj and IsPositionalObjectRep, [] );
+   IsVectorObj and IsPositionalObjectRep and IsNoImmediateMethodsObject, [] );
 
 
 #############################################################################
@@ -60,14 +60,15 @@ DeclareRepresentation( "IsPlistVectorRep",
 ##  a list of its rows, in the sense defined in
 ##  Section <Ref Sect="Operations for Row List Matrix Objects"/>.
 ##  It is internally represented as a positional object
-##  (see <Ref Filt="IsPositionalObjectRep"/> that stores 4 entries:
+##  (see <Ref Filt="IsPositionalObjectRep"/> that stores four entries:
 ##  <Enum>
 ##  <Item>
 ##    its base domain
 ##    (see <Ref Attr="BaseDomain" Label="for a matrix object"/>),
 ##  </Item>
 ##  <Item>
-##    an empty vector in the representation of each row,,
+##    the number of rows
+##    (see <Ref Attr="NumberRows" Label="for a matrix object"/>), and
 ##  </Item>
 ##  <Item>
 ##    the number of columns
@@ -83,28 +84,20 @@ DeclareRepresentation( "IsPlistVectorRep",
 ##  <#/GAPDoc>
 ##
 DeclareRepresentation( "IsPlistMatrixRep",
-   IsRowListMatrix and IsPositionalObjectRep, [] );
+   IsRowListMatrix and IsPositionalObjectRep and IsNoImmediateMethodsObject, [] );
 
 
 # Some constants for matrix access:
-BindGlobal( "BDPOS", 1 );
-BindGlobal( "EMPOS", 2 );
-BindGlobal( "RLPOS", 3 );
-BindGlobal( "ROWSPOS", 4 );
+# TODO rename these so that one can quickly see that they belong to IsPlist*Rep
+BindConstant( "BDPOS", 1 );
+BindConstant( "NUM_ROWS_POS", 2 );
+BindConstant( "NUM_COLS_POS", 3 );
+BindConstant( "ROWSPOS", 4 );
 
 # For vector access:
-#BindGlobal( "BDPOS", 1 );   # see above
-BindGlobal( "ELSPOS", 2 );
+#BindConstant( "BDPOS", 1 );   # see above
+BindConstant( "ELSPOS", 2 );
 
 # Two filters to speed up some methods:
 DeclareFilter( "IsIntVector" );
 DeclareFilter( "IsFFEVector" );
-
-############################################################################
-# Constructors:
-############################################################################
-
-#T Should this be documented?
-#T It seems to be just an auxiliary function for the documented constructors.
-DeclareGlobalFunction( "MakePlistVectorType" );
-