LibGfx: Add v2 "ncol" tag, expand comment

I had missed this in 21cc0c0cb2f because this tag is missing in
"Table 32 — Tag list" in the v2 ICC spec O_o. But it's in
"6.4.26 namedColorTag".

Also add a comment pointing to a page saying that all these tags
are very deprecated and not even recommended for new v2 profiles.
(That's how I noticed that namedColorTag was missing.)

Userland/Libraries/LibGfx/ICC/Profile.cpp

@@ -1294,6 +1294,8 @@ ErrorOr<void> Profile::check_tag_types()
     //   "Tag Type: deviceSettingsType"
     // - ICC v2, 6.4.24 mediaBlackPointTag
     //   "Tag Type: XYZType"
+    // - ICC v2, 6.4.26 namedColorTag
+    //   "Tag Type: namedColorType"
     // - ICC v2, 6.4.34 ps2CRD0Tag
     //   "Tag Type: dataType"
     // - ICC v2, 6.4.35 ps2CRD1Tag
@@ -1312,6 +1314,9 @@ ErrorOr<void> Profile::check_tag_types()
     //   "Tag Type: screeningType"
     // - ICC v2, 6.4.45 ucrbgTag
     //   "Tag Type: ucrbgType"
+    // https://www.color.org/v2profiles.xalter says about these tags:
+    // "it is also recommended that optional tags in the v2 specification that have subsequently become
+    //  obsolete are not included in future profiles made to the v2 specification."
 
     return {};
 }

Userland/Libraries/LibGfx/ICC/Tags.h

@@ -69,6 +69,7 @@ namespace Gfx::ICC {
     TAG(crdInfoTag, 0x63726469 /* 'crdi' */)                        \
     TAG(deviceSettingsTag, 0x64657673 /* 'devs' */)                 \
     TAG(mediaBlackPointTag, 0x626B7074 /* 'bkpt' */)                \
+    TAG(namedColorTag, 0x6E636F6C /* 'ncol' */)                     \
     TAG(ps2CRD0Tag, 0x70736430 /* 'psd0' */)                        \
     TAG(ps2CRD1Tag, 0x70736431 /* 'psd1' */)                        \
     TAG(ps2CRD2Tag, 0x70736432 /* 'psd2' */)                        \