refactor(core): remove unused i18n placeholder for projection (#39172)

Runtime i18n logic doesn't distinguish `<ng-content>` tag placeholders and regular element tag
placeholders in i18n messages, so there is no need to have a special marker for projection-based
placeholders and element markers can be used instead.

PR Close #39172

packages/compiler/src/render3/view/i18n/context.ts

@@ -15,7 +15,6 @@ import {assembleBoundTextPlaceholders, getSeqNumberGenerator, updatePlaceholderM
 enum TagType {
   ELEMENT,
   TEMPLATE,
-  PROJECTION
 }
 
 /**
@@ -105,10 +104,12 @@ export class I18nContext {
     this.appendTag(TagType.ELEMENT, node as i18n.TagPlaceholder, index, closed);
   }
   appendProjection(node: i18n.I18nMeta, index: number) {
-    // add open and close tags at the same time,
-    // since we process projected content separately
-    this.appendTag(TagType.PROJECTION, node as i18n.TagPlaceholder, index, false);
-    this.appendTag(TagType.PROJECTION, node as i18n.TagPlaceholder, index, true);
+    // Add open and close tags at the same time, since `<ng-content>` has no content,
+    // so when we come across `<ng-content>` we can register both open and close tags.
+    // Note: runtime i18n logic doesn't distinguish `<ng-content>` tag placeholders and
+    // regular element tag placeholders, so we generate element placeholders for both types.
+    this.appendTag(TagType.ELEMENT, node as i18n.TagPlaceholder, index, false);
+    this.appendTag(TagType.ELEMENT, node as i18n.TagPlaceholder, index, true);
   }
 
   /**
@@ -215,9 +216,6 @@ function serializePlaceholderValue(value: any): string {
     case TagType.TEMPLATE:
       return template(value, value.closed);
 
-    case TagType.PROJECTION:
-      return projection(value, value.closed);
-
     default:
       return value;
   }

packages/core/src/render3/i18n/i18n_parse.ts

@@ -39,7 +39,7 @@ const ICU_BLOCK_REGEXP = /^\s*(�\d+:?\d*�)\s*,\s*(select|plural)\s*,/;
 
 const MARKER = `�`;
 const SUBTEMPLATE_REGEXP = /�\/?\*(\d+:\d+)�/gi;
-const PH_REGEXP = /�(\/?[#*!]\d+):?\d*�/gi;
+const PH_REGEXP = /�(\/?[#*]\d+):?\d*�/gi;
 
 /**
  * Angular Dart introduced &ngsp; as a placeholder for non-removable space, see:
@@ -120,7 +120,7 @@ export function i18nStartFirstCreatePass(
       // At this point value is something like: '/#1:2' (originally coming from '�/#1:2�')
       const isClosing = value.charCodeAt(0) === CharCode.SLASH;
       const type = value.charCodeAt(isClosing ? 1 : 0);
-      ngDevMode && assertOneOf(type, CharCode.STAR, CharCode.HASH, CharCode.EXCLAMATION);
+      ngDevMode && assertOneOf(type, CharCode.STAR, CharCode.HASH);
       const index = HEADER_OFFSET + Number.parseInt(value.substring((isClosing ? 2 : 1)));
       if (isClosing) {
         existingTNodeStack.shift();

packages/core/src/util/char_code.ts

@@ -12,7 +12,6 @@
 export const enum CharCode {
   UPPER_CASE = ~32,   // & with this will make the char uppercase
   SPACE = 32,         // " "
-  EXCLAMATION = 33,   // "!"
   DOUBLE_QUOTE = 34,  // "\""
   HASH = 35,          // "#"
   SINGLE_QUOTE = 39,  // "'"