Fix two auto-indent issues with Markdown and YAML (#20193)

Closes #13376
Closes #13338

Release Notes:

- Fixed unhelpful auto-indent suggestions in markdown.
- Added `auto_indent_on_paste` setting, which can be used on a
per-language basis, to configure whether indentation should be adjusted
when pasting. This setting is enabled by default for languages other
than YAML and Markdown.

crates/language/src/language.rs

@@ -591,6 +591,9 @@ pub struct LanguageConfig {
     /// the indentation level for a new line.
     #[serde(default = "auto_indent_using_last_non_empty_line_default")]
     pub auto_indent_using_last_non_empty_line: bool,
+    // Whether indentation of pasted content should be adjusted based on the context.
+    #[serde(default)]
+    pub auto_indent_on_paste: Option<bool>,
     /// A regex that is used to determine whether the indentation level should be
     /// increased in the following line.
     #[serde(default, deserialize_with = "deserialize_regex")]
@@ -718,6 +721,7 @@ impl Default for LanguageConfig {
             matcher: LanguageMatcher::default(),
             brackets: Default::default(),
             auto_indent_using_last_non_empty_line: auto_indent_using_last_non_empty_line_default(),
+            auto_indent_on_paste: None,
             increase_indent_pattern: Default::default(),
             decrease_indent_pattern: Default::default(),
             autoclose_before: Default::default(),