Implement remaining rounding to increment methods (#4246)

With `trunc_to_increment` and `expand_to_increment` implemented, this
finishes implementing the rest of the rounding methods.

CHANGELOG.md

@@ -36,7 +36,7 @@
         - Add implementations for `HashSet`, `HashMap`, `BTreeSet`, `BTreeMap` (https://github.com/unicode-org/icu4x/pull/4268, https://github.com/unicode-org/icu4x/pull/4274, https://github.com/unicode-org/icu4x/pull/4295)  
         - Improvements to `databake::test_bake!()` (https://github.com/unicode-org/icu4x/pull/4182)
     - `fixed_decimal`
-        - Experimental rounding increment support (https://github.com/unicode-org/icu4x/pull/4219)
+        - Experimental rounding increment support (https://github.com/unicode-org/icu4x/pull/4219, https://github.com/unicode-org/icu4x/pull/4246)
     - `litemap`
         - Implement `databake::Bake` on `LiteMap` (https://github.com/unicode-org/icu4x/pull/4275)
     - `tinystr`

tools/ffi_coverage/src/allowlist.rs

@@ -317,6 +317,20 @@ lazy_static::lazy_static! {
         "fixed_decimal::FixedDecimal::expanded_to_increment",
         "fixed_decimal::FixedDecimal::trunc_to_increment",
         "fixed_decimal::FixedDecimal::trunced_to_increment",
+        "fixed_decimal::FixedDecimal::ceil_to_increment",
+        "fixed_decimal::FixedDecimal::ceiled_to_increment",
+        "fixed_decimal::FixedDecimal::floor_to_increment",
+        "fixed_decimal::FixedDecimal::floored_to_increment",
+        "fixed_decimal::FixedDecimal::half_ceil_to_increment",
+        "fixed_decimal::FixedDecimal::half_ceiled_to_increment",
+        "fixed_decimal::FixedDecimal::half_even_to_increment",
+        "fixed_decimal::FixedDecimal::half_evened_to_increment",
+        "fixed_decimal::FixedDecimal::half_expand_to_increment",
+        "fixed_decimal::FixedDecimal::half_expanded_to_increment",
+        "fixed_decimal::FixedDecimal::half_floor_to_increment",
+        "fixed_decimal::FixedDecimal::half_floored_to_increment",
+        "fixed_decimal::FixedDecimal::half_trunc_to_increment",
+        "fixed_decimal::FixedDecimal::half_trunced_to_increment",
 
         // Stuff that does not need to be exposed over FFI
         // Especially for stuff that are Rust specific like conversion traits