%define lr.type: make values lowercase IDs.

%define lr.type: make values lowercase IDs.

That is, "LALR" => "lalr", "IELR" => "ielr", and
"canonical LR" => "canonical-lr".
* NEWS (2.5): Update documentation.
* doc/bison.texinfo (Decl Summary): Likewise.
* src/ielr.c (ielr): Use new values.
* src/ielr.h (ielr): Update documentation.
* src/reader.c (prepare_percent_define_front_end_variables): Use
and validate new values.
* tests/existing.at (AT_TEST_EXISTING_GRAMMAR): Update test
grammars.
* tests/reduce.at (AT_TEST_LR_TYPE): Likewise.
(cherry picked from commit 6ba9640406758718fdcfb7a1154e58ce4d9b196c)