vim-patch:8.2.4883: string interpolation only works in heredoc

Problem:    String interpolation only works in heredoc.
Solution:   Support interpolated strings.  Use syntax for heredoc consistent
            with strings, similar to C#. (closes vim/vim#10327)

https://github.com/vim/vim/commit/2eaef106e4a7fc9dc74a7e672b5f550ec1f9786e

Cherry-pick Test_Debugger_breakadd_expr() from Vim.

Co-authored-by: LemonBoy <thatlemon@gmail.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index c8eea03f5f..518a190d3c 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1407,6 +1407,26 @@ to be doubled.  These two commands are equivalent: >
 
 
 ------------------------------------------------------------------------------
+interpolated-string					*interp-string*
+
+$"string"		interpolated string constant		*expr-$quote*
+$'string'		interpolated literal string constant	*expr-$'*
+
+Interpolated strings are an extension of the |string| and |literal-string|,
+allowing the inclusion of Vim script expressions (see |expr1|).  Any
+expression returning a value can be enclosed between curly braces.  The value
+is converted to a string.  All the text and results of the expressions
+are concatenated to make a new string.
+
+To include an opening brace '{' or closing brace '}' in the string content
+double it.
+
+Examples: >
+	let your_name = input("What's your name? ")
+	echo $"Hello, {your_name}!"
+	echo $"The square root of 9 is {sqrt(9)}"
+
+------------------------------------------------------------------------------
 option						*expr-option* *E112* *E113*
 
 &option			option value, local value if possible