Format spaces inside curly braces in string template

Fixes #KT-12791

idea/formatter/src/org/jetbrains/kotlin/idea/formatter/kotlinSpacingRules.kt

@@ -214,6 +214,9 @@ fun createSpacingBuilder(settings: CodeStyleSettings, builderUtil: KotlinSpacing
             betweenInside(LPAR, DESTRUCTURING_DECLARATION, FOR).spaces(0)
             betweenInside(LOOP_RANGE, RPAR, FOR).spaces(0)
 
+            after(LONG_TEMPLATE_ENTRY_START).spaces(0)
+            before(LONG_TEMPLATE_ENTRY_END).spaces(0)
+
             val TYPE_COLON_ELEMENTS = TokenSet.create(PROPERTY, FUN, VALUE_PARAMETER, DESTRUCTURING_DECLARATION_ENTRY, FUNCTION_LITERAL)
             beforeInside(COLON, TYPE_COLON_ELEMENTS) { spaceIf(kotlinSettings.SPACE_BEFORE_TYPE_COLON) }
             afterInside(COLON, TYPE_COLON_ELEMENTS) { spaceIf(kotlinSettings.SPACE_AFTER_TYPE_COLON) }

idea/testData/formatter/CurlyBraceStringInterpolation.after.kt

@@ -0,0 +1,3 @@
+fun foo() {
+    "${1}"
+}

idea/testData/formatter/CurlyBraceStringInterpolation.kt

@@ -0,0 +1,3 @@
+fun foo() {
+    "${ 1 }"
+}

idea/tests/org/jetbrains/kotlin/formatter/FormatterTestGenerated.java

@@ -151,6 +151,12 @@ public class FormatterTestGenerated extends AbstractFormatterTest {
             doTest(fileName);
         }
 
+        @TestMetadata("CurlyBraceStringInterpolation.after.kt")
+        public void testCurlyBraceStringInterpolation() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/formatter/CurlyBraceStringInterpolation.after.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("DelegationList.after.kt")
         public void testDelegationList() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/formatter/DelegationList.after.kt");