language: Fix indent suggestions for significant indented languages like Python (#29625)

Closes #26157

This fixes multiple cases where Python indentation breaks:
- [x] Adding a new line after `if`, `try`, etc. correctly indents in
that scope
- [x] Multi-cursor tabs correctly preserve relative indents
- [x] Adding a new line after `else`, `finally`, etc. correctly outdents
them
- [x] Existing Tests

Future Todo: I need to add new tests for all the above cases.

Before/After:

1. Multi-cursor tabs correctly preserve relative indents


https://github.com/user-attachments/assets/08a46ddf-5371-4e26-ae7d-f8aa0b31c4a2

2. Adding a new line after `if`, `try`, etc. correctly indents in that
scope


https://github.com/user-attachments/assets/9affae97-1a50-43c9-9e9f-c1ea3a747813

Release Notes:

- Fixes indentation-related issues involving tab, newline, etc for
Python.

crates/language/src/language.rs

@@ -681,6 +681,10 @@ pub struct LanguageConfig {
     #[serde(default)]
     #[schemars(schema_with = "bracket_pair_config_json_schema")]
     pub brackets: BracketPairConfig,
+    /// If set to true, indicates the language uses significant whitespace/indentation
+    /// for syntax structure (like Python) rather than brackets/braces for code blocks.
+    #[serde(default)]
+    pub significant_indentation: bool,
     /// If set to true, auto indentation uses last non empty line to determine
     /// the indentation level for a new line.
     #[serde(default = "auto_indent_using_last_non_empty_line_default")]
@@ -884,6 +888,7 @@ impl Default for LanguageConfig {
             jsx_tag_auto_close: None,
             completion_query_characters: Default::default(),
             debuggers: Default::default(),
+            significant_indentation: Default::default(),
         }
     }
 }