https://bugs.freedesktop.org/show_bug.cgi?id=53233

Implemented for Arabic, Hebrew, and generic marks.
Activated if no GPOS table present.

Used when there is no GPOS.

Fixes logic also, where before we were always matching if glyphs_len==1
and a ligature started with the glyph.

'rclt' is "Required Contextual Forms" being proposed by Microsoft.
It's like 'calt', but supposedly always on.  We apply 'calt' anyway,
and now apply this too.

Lifted from https://bugzilla.mozilla.org/show_bug.cgi?id=728866

...again.

Patch from Martin Hosken.

We already set recount to INVALID when destroying.
This block was not necessary.

We don't apply them together anyway.  Should not make any difference
right now.

Lohit Devanagari has a glyph named:
u0924_u094D.half_u0930_u094D.blwf.vatu

Such it wouldn't apply to pointers accidentally.

Oops.  I broken this badly and the test suite did not notice.  That
worries me.  Have to investigate.

At this point, the GDEF glyph synthesis looks pointless.  Not that I
have many fonts without GDEF lying around.

As for mark advance zeroing when GPOS not available, that also is being
replaced by proper fallback mark positioning soon.

This concludes the Indic shape_plan work.  May do for Arabic also...