Implement PackedPatternsV1 with packing and unpacking (#5580)

Part of #257

components/datetime/src/pattern/runtime/pattern.rs

@@ -7,6 +7,7 @@
 use super::super::{reference, PatternError, PatternItem, TimeGranularity};
 use alloc::vec::Vec;
 use core::str::FromStr;
+use icu_plurals::provider::FourBitMetadata;
 use icu_provider::prelude::*;
 use zerovec::{ule::AsULE, ZeroSlice, ZeroVec};
 
@@ -75,6 +76,15 @@ impl PatternMetadata {
     pub(crate) fn set_time_granularity(&mut self, time_granularity: TimeGranularity) {
         self.0 = time_granularity.ordinal();
     }
+
+    pub(crate) fn to_four_bit_metadata(self) -> FourBitMetadata {
+        #[allow(clippy::unwrap_used)] // valid values for self.0 are 0, 1, 2, 3, or 4
+        FourBitMetadata::try_from_byte(self.0).unwrap()
+    }
+
+    pub(crate) fn from_u8(other: u8) -> Self {
+        Self(TimeGranularity::from_ordinal(other).ordinal())
+    }
 }
 
 impl Default for PatternMetadata {

components/datetime/src/provider/mod.rs

@@ -17,6 +17,7 @@
 
 pub mod calendar;
 pub(crate) mod date_time;
+pub mod packed_pattern;
 pub mod time_zones;
 
 /// Module for new DateSymbols design