Strings from builtin functions should be null terminated if needed

[Vexu]

@embedFile, @errorName, @memberName, @tagName and @typeName should be able to return null terminated slices so this would work:

const name: [*:0]u8 = @tagName(E.SomeEnum);

[andrewrk]

They should also be updated to return pointers to arrays rather than slices when the length is comptime known. It goes along with the same ideas behind #863.

[jmc-88]

For the record, @memberName was removed in 45da72c and 3458fb8, though there's still a reference to it in a commented out code block:

zig/lib/std/event/channel.zig

Line 142 in 85755c5

// return @unionInit(EnumUnion, @memberName(EnumUnion, 0), result);

[jmc-88]

Now that #9183 too has been merged, I think the only outstanding builtin would be @typeInfo(), which has been forked to #9182. Maybe this can be closed?