Auto merge of #16618 - DropDemBits:structured-snippet-fix-escape-left-curly, r=Veykril

fix: Don't add `\` before `{`

Fixes #16607 for `{`. The `}` case is already fixed by #16475.

The [LSP snippet grammar](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#snippet_syntax) only specifies that `$`, `}`, and `\` can be escaped with backslashes, but not `{`.

Author: bors

crates/rust-analyzer/src/lsp/to_proto.rs

@@ -1003,7 +1003,7 @@ fn merge_text_and_snippet_edits(
 
             // find which snippet bits need to be escaped
             let escape_places = new_text
-                .rmatch_indices(['\\', '$', '{', '}'])
+                .rmatch_indices(['\\', '$', '}'])
                 .map(|(insert, _)| insert)
                 .collect_vec();
             let mut escape_places = escape_places.into_iter().peekable();
@@ -2176,7 +2176,7 @@ fn bar(_: usize) {}
                                 character: 0,
                             },
                         },
-                        new_text: "\\$${1:ab\\{\\}\\$c\\\\d}ef",
+                        new_text: "\\$${1:ab{\\}\\$c\\\\d}ef",
                         insert_text_format: Some(
                             Snippet,
                         ),
@@ -2272,7 +2272,7 @@ struct ProcMacro {
                                 character: 5,
                             },
                         },
-                        new_text: "$0disabled = false;\n    ProcMacro \\{\n        disabled,\n    \\}",
+                        new_text: "$0disabled = false;\n    ProcMacro {\n        disabled,\n    \\}",
                         insert_text_format: Some(
                             Snippet,
                         ),
@@ -2336,7 +2336,7 @@ struct P {
                                 character: 5,
                             },
                         },
-                        new_text: "$0disabled = false;\n    ProcMacro \\{\n        disabled,\n    \\}",
+                        new_text: "$0disabled = false;\n    ProcMacro {\n        disabled,\n    \\}",
                         insert_text_format: Some(
                             Snippet,
                         ),
@@ -2401,7 +2401,7 @@ struct ProcMacro {
                                 character: 5,
                             },
                         },
-                        new_text: "${0:disabled} = false;\n    ProcMacro \\{\n        disabled,\n    \\}",
+                        new_text: "${0:disabled} = false;\n    ProcMacro {\n        disabled,\n    \\}",
                         insert_text_format: Some(
                             Snippet,
                         ),
@@ -2466,7 +2466,7 @@ struct P {
                                 character: 5,
                             },
                         },
-                        new_text: "${0:disabled} = false;\n    ProcMacro \\{\n        disabled,\n    \\}",
+                        new_text: "${0:disabled} = false;\n    ProcMacro {\n        disabled,\n    \\}",
                         insert_text_format: Some(
                             Snippet,
                         ),