Integrate MonthCode into public API and related adjustments (#208)

This change integrate `MonthCode` into the public API of the partial
fields and `month_code` methods in order to better represent
[PrepareCalendarFields](https://tc39.es/proposal-temporal/#sec-temporal-preparecalendarfields)
conversion.

This does also add a host of public APIs to `MonthCode` for interacting
with it and adjusts the general validation methods (although, I do
suspect this will need to be iterated on in the future to better support
more calendars).

CC: @Manishearth as this includes updates to `temporal_capi`

Author: nekevss

src/builtins/compiled/zoneddatetime.rs

@@ -5,7 +5,7 @@ use crate::{
         ArithmeticOverflow, DifferenceSettings, Disambiguation, DisplayCalendar, DisplayOffset,
         DisplayTimeZone, OffsetDisambiguation, ToStringRoundingOptions,
     },
-    Duration, PlainDate, PlainDateTime, PlainTime, TemporalError, TemporalResult,
+    Duration, MonthCode, PlainDate, PlainDateTime, PlainTime, TemporalError, TemporalResult,
 };
 use alloc::string::String;
 use tinystr::TinyAsciiStr;
@@ -58,7 +58,7 @@ impl ZonedDateTime {
     /// Returns the `ZonedDateTime`'s calendar month code.
     ///
     /// Enable with the `compiled_data` feature flag.
-    pub fn month_code(&self) -> TemporalResult<TinyAsciiStr<4>> {
+    pub fn month_code(&self) -> TemporalResult<MonthCode> {
         let provider = TZ_PROVIDER
             .lock()
             .map_err(|_| TemporalError::general("Unable to acquire lock"))?;

src/builtins/core/calendar.rs

@@ -35,8 +35,8 @@ use super::{PartialDate, ZonedDateTime};
 mod era;
 mod types;
 
-pub(crate) use types::{ascii_four_to_integer, month_to_month_code};
-pub use types::{ResolveType, ResolvedCalendarFields};
+pub(crate) use types::{month_to_month_code, ResolutionType};
+pub use types::{MonthCode, ResolvedCalendarFields};
 
 use era::EraInfo;
 
@@ -222,13 +222,13 @@ impl Calendar {
         overflow: ArithmeticOverflow,
     ) -> TemporalResult<PlainDate> {
         let resolved_fields =
-            ResolvedCalendarFields::try_from_partial(partial, overflow, ResolveType::Date)?;
+            ResolvedCalendarFields::try_from_partial(partial, overflow, ResolutionType::Date)?;
 
         if self.is_iso() {
             // Resolve month and monthCode;
             return PlainDate::new_with_overflow(
                 resolved_fields.era_year.year,
-                resolved_fields.month_code.as_iso_month_integer()?,
+                resolved_fields.month_code.to_month_integer(),
                 resolved_fields.day,
                 self.clone(),
                 overflow,
@@ -261,10 +261,10 @@ impl Calendar {
         overflow: ArithmeticOverflow,
     ) -> TemporalResult<PlainMonthDay> {
         let resolved_fields =
-            ResolvedCalendarFields::try_from_partial(partial, overflow, ResolveType::MonthDay)?;
+            ResolvedCalendarFields::try_from_partial(partial, overflow, ResolutionType::MonthDay)?;
         if self.is_iso() {
             return PlainMonthDay::new_with_overflow(
-                resolved_fields.month_code.as_iso_month_integer()?,
+                resolved_fields.month_code.to_month_integer(),
                 resolved_fields.day,
                 self.clone(),
                 overflow,
@@ -284,11 +284,11 @@ impl Calendar {
         overflow: ArithmeticOverflow,
     ) -> TemporalResult<PlainYearMonth> {
         let resolved_fields =
-            ResolvedCalendarFields::try_from_partial(partial, overflow, ResolveType::YearMonth)?;
+            ResolvedCalendarFields::try_from_partial(partial, overflow, ResolutionType::YearMonth)?;
         if self.is_iso() {
             return PlainYearMonth::new_with_overflow(
                 resolved_fields.era_year.year,
-                resolved_fields.month_code.as_iso_month_integer()?,
+                resolved_fields.month_code.to_month_integer(),
                 Some(resolved_fields.day),
                 self.clone(),
                 overflow,
@@ -398,12 +398,13 @@ impl Calendar {
     }
 
     /// `CalendarMonthCode`
-    pub fn month_code(&self, iso_date: &IsoDate) -> TemporalResult<TinyAsciiStr<4>> {
+    pub fn month_code(&self, iso_date: &IsoDate) -> TemporalResult<MonthCode> {
         if self.is_iso() {
-            return Ok(iso_date.as_icu4x()?.month().standard_code.0);
+            let mc = iso_date.as_icu4x()?.month().standard_code.0;
+            return Ok(MonthCode(mc));
         }
         let calendar_date = self.0.date_from_iso(iso_date.as_icu4x()?);
-        Ok(self.0.month(&calendar_date).standard_code.0)
+        Ok(MonthCode(self.0.month(&calendar_date).standard_code.0))
     }
 
     /// `CalendarDay`