Parsing: make parse syntax a per-parse value, drop ModeInterface

The active parse's syntax flavour is a per-parse question, not process-
global state: within a single request a plugin can render bun

Parsing: make parse syntax a per-parse value, drop ModeInterface

The active parse's syntax flavour is a per-parse question, not process-
global state: within a single request a plugin can render bundled
DokuWiki-syntax text inside an otherwise-Markdown page. Yet ModeRegistry
was a singleton that read $conf['syntax'] and the $PARSER_MODES global,
and every mode reached it through ModeRegistry::getInstance() — so the
flavour lived in shared mutable state that two parses in one request
would fight over.

Make the registry a short-lived value instead:

- ModeRegistry is constructed once per parse with an explicit $syntax
and injected into Parser, Handler and every mode. getSyntax() /
isDwPreferred() / isMdPreferred() consult $this->syntax; the
DOKU_UNITTEST-gated mode-list cache hack is gone (each registry is
fresh, nothing to invalidate).
- p_get_instructions() is now the single place in the pipeline where
$conf['syntax'] is read; from there the flavour travels as a
parameter. No code under inc/Parsing/ reads $conf['syntax'] directly
anymore — the five syntax-reading modes (Preformatted, GfmHr,
GfmEscape, Externallink, GfmQuote) route through $this->registry.

Keep the two concepts apart, as documented in the ModeRegistry and
AbstractMode docblocks: the user's configured *preference* stays in
$conf['syntax'] for UI code (toolbar, settings), while the active
parse's syntax is a parameter carried by the registry.

$PARSER_MODES is demoted to a deprecated, read-only mirror, published
during loadPluginModes() — third-party syntax plugins (columnlist,
alphalist2, phpwikify, skipentity) and the bundled info plugin read the
global directly, often from their constructors, so the taxonomy must
stay visible there. No core code reads the mirror.

Fold ModeInterface into AbstractMode while here: getSort()/handle() are
abstract, the connect callbacks carry defaults, and the public $Lexer
"FIXME should be done by setter" becomes setLexer()/getLexer() injected
by Parser::addMode() alongside the registry. Nested-content resolution
moves to the allowedCategories()/filterAllowedModes() hooks, resolved
once when the registry is attached.

Tests build their own parser/registry through ParserTestBase::setSyntax()
instead of mutating $conf and calling the removed ModeRegistry::reset().

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GfmQuote: accept ^> line starts so quotes can follow tables and lists

GfmTable, DW Table, and DW Listblock all consume the boundary \n on
their way out. A pure-lookahead exit pattern at that boundar

GfmQuote: accept ^> line starts so quotes can follow tables and lists

GfmTable, DW Table, and DW Listblock all consume the boundary \n on
their way out. A pure-lookahead exit pattern at that boundary would
trip the lexer's no-advance safety check, because tables and lists
exit right after consuming a marker token and have no leading
unmatched content for the lookahead to attach to (unlike Preformatted,
whose body leaves code lines as UNMATCHED right before the boundary).

Fix this on the consumer side: change the first-line anchor from \n>
to (?:^|\n)>. With the lexer's m flag, ^ matches at offset 0 and at
any position immediately following a \n in the subject, including the
position right after a \n that a preceding mode just consumed.
Subsequent quote lines keep the \n> anchor.

Adds three handoff tests in GfmQuoteTest covering GfmTable, DW Table,
and DW Listblock. Resolves GFM spec example 201.

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rename syntax flavors 'dokuwiki' / 'markdown' to 'dw' / 'md'

Symmetry with the existing 'dw+md' / 'md+dw' setting values.

replace DW Quote with unified GfmQuote

GfmQuote covers blockquote parsing for both DokuWiki and GFM dialects
in a single mode. Same quote_open/quote_close handler instructions; a
DW-preferred post-p

replace DW Quote with unified GfmQuote

GfmQuote covers blockquote parsing for both DokuWiki and GFM dialects
in a single mode. Same quote_open/quote_close handler instructions; a
DW-preferred post-pass flattens sub-parsed paragraph wrapping into
linebreak calls so existing pages keep their <br/>-between-lines
rendering. MD-preferred keeps the <p>-wrapped spec shape.

Block content (lists, fenced code, tables) inside `>` quotes now
renders, since the body is sub-parsed. Headers stay excluded
(BASEONLY) — TOC and section-edit anchors don't compose with
<blockquote>, same rationale as GfmListblock.

Convert ModeRegistry's sub-parser cache into an acquire/release pool
to support same-key re-entrancy: a list inside a quote re-enters
gfm_quote during the list-item sub-parse, and the inner call needs
its own parser instance even though the exclusion key matches.
GfmListblock is updated to use the new acquire/release primitives.

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