MSBuild 3-Letter Language Code Issue

This is a repro demonstrating that MSBuild does not copy resource files with 3-letter language codes to the build/publish output.

1. Build ProjectA. It will create a ProjectA.1.0.0.nupkg file in the repo root.
2. Check the contents of ProjectA.1.0.0.nupkg. Both en and agq languages are present, as expected.
3. Build ProjectB.
4. Check the build output. Only en is present, agq is not.

We are also seeing this occur with dotnet publish and with thePackAsTool option.

The following neutral cultures are confirmed to be failing:

agq ars asa ast bas bem bez brx ccp cgg chr ckb dav dje dsb dua dyo ebu ewo fil fur gsw guz haw hsb jgo jmc kab kam kde kea khq kkj kln kok ksb ksf ksh lag lkt lrc luo luy mas mer mfe mgh mgo mua mzn naq nds nmg nnh nus nyn qu rof rwk sah saq sbp seh ses shi shi-Latn shi-Tfng smn teo twq tzm vai vai-Latn vai-Vaii vun wae xog yav zgh

Presumably, the specific variants are also failing, but we haven't confirmed.