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_settings.rs

@@ -125,6 +125,8 @@ pub struct LanguageSettings {
     /// Whether to use additional LSP queries to format (and amend) the code after
     /// every "trigger" symbol input, defined by LSP server capabilities.
     pub use_on_type_format: bool,
+    /// Whether indentation of pasted content should be adjusted based on the context.
+    pub auto_indent_on_paste: bool,
     // Controls how the editor handles the autoclosed characters.
     pub always_treat_brackets_as_autoclosed: bool,
     /// Which code actions to run on save
@@ -360,6 +362,10 @@ pub struct LanguageSettingsContent {
     ///
     /// Default: true
     pub linked_edits: Option<bool>,
+    /// Whether indentation of pasted content should be adjusted based on the context.
+    ///
+    /// Default: true
+    pub auto_indent_on_paste: Option<bool>,
     /// Task configuration for this language.
     ///
     /// Default: {}
@@ -1132,6 +1138,7 @@ fn merge_settings(settings: &mut LanguageSettings, src: &LanguageSettingsContent
     merge(&mut settings.use_autoclose, src.use_autoclose);
     merge(&mut settings.use_auto_surround, src.use_auto_surround);
     merge(&mut settings.use_on_type_format, src.use_on_type_format);
+    merge(&mut settings.auto_indent_on_paste, src.auto_indent_on_paste);
     merge(
         &mut settings.always_treat_brackets_as_autoclosed,
         src.always_treat_brackets_as_autoclosed,