Reviewers

None

Bugzilla Bug ID

2048060

Under the L4 (P-style A) gate, these two fonts ended up with allowed
locale sets that cover the bulk of the BCP-47 tag universe (135/192 =
70% for simsun-extg, 106/192 = 55% for nirmala text - 115 and 106
distinct language prefixes respectively). Locale-gating a font that's
allowed for ~half-plus of all locales is essentially a no-op: the gate
fires for so few users that it provides almost no entropy reduction
while still costing ~240 FONT_RULE tag entries in the source.

Promote both to the unconditional kLangPackFonts list and drop their
corresponding FONT_RULE blocks. LangPack tier (rather than Base) means
the fonts are visible at the default font-visibility=3 pref and at
font-visibility=2 (restricted/ETP-Strict modes) but still hidden at
font-visibility=1 / RFP, preserving the fingerprinting protection at
that bar without the redundant per-locale gating cost.

Because kLangPackFonts is no longer empty, the CheckFamilyList /
FamilyInList / std::size references in gfxDWriteFontList that the
previous commit had to remove (zero-length array templates) are
restored to their pre-Bug 2048060 form.

The remaining 98 L4-gated fonts (median 2 tags, max 41) still earn the
locale gate.