Faitfhful handling of the_toks (#1335)
* upgrades to \meaning, \show-like macros, writableTokens
* add pdftex \expanded test
* a first proof-of-concept for THE_TOKS via flaging in the Gullet pushback
* move away from EExpanded and the like
* new multi_escaped_param sanity test
* introducing CC_ARG; back to parity with main test suite
* param collapsing on Expandable creation, all tests pass including first expl3 subtest
* X_THE check should be for underlying definition (cover \let macros)
* cleanup: drop unneeded message from test
* first operational the_marks prototype, ok upto line 9000 in expl3-code.tex
* missing index increment; upto line 11,351 in expl3-code
* reintroduce optimization for on-demand tokenization of string Expandable definitions
* some more missing registers from eTeX needed in expl3
* cleanup Parameters changes
* Consistent naming for tables indexed by catcodes: CATCODE_WHATEVER, upcase
* And extend some overlooked tables
* remove trivial_expansion from Expandable
* rename and clarify expl-adapted param tokens passing test
* clarifying comment
* fix broken patch of neutralize
* Alternative approach to marking deferred expansion (for \the): Use a new catcode
* Use $LaTeXML::KEEP_THE *only* in DefExpanded to make clear that that's the onlyu
context from which NOEXPAND1 can be *released* by gullet.
(readXToken expanding \the,\detokenize,\unexpanded are the only place
they are created).
Probably should do a cleanup pass on naming re: NOEXPAND1, (with|without|get)_dont_expand
* trim down use of CC_NOEXPAND1 to the hot paths of DefExpanded and DefPlain
* remove another unnecessary guard
* two paranoid Fatal errors in case we let a \the-mask slip through
* add comments, rely on PrepArgTokens for removing flags
* Use DefPlain instead of PrepArgTokens
* Move PrepArgTokens to Tokens->packParameters
* More consistent naming for variables/constants involving 'smuggling' \the expansions
* Make macrobody option for DefParameter do packParameter; more consistent(?) use of packParameter
* rename new parameter option to packParameters
Co-authored-by: Bruce Miller <email address hidden>