Remove TextEmitter (#20595)

## Summary

Addresses
https://github.com/astral-sh/ruff/pull/20443#discussion_r2381237640 by
factoring out the `match` on the ruff output format in a way that should
be reusable by the formatter.

I didn't think this was going to work at first, but the fact that the
config holds options that apply only to certain output formats works in
our favor here. We can set up a single config for all of the output
formats and then use `try_from` to convert the `OutputFormat` to a
`DiagnosticFormat` later.

## Test Plan

Existing tests, plus a few new ones to make sure relocating the
`SHOW_FIX_SUMMARY` rendering worked, that was untested before. I deleted
a bunch of test code along with the `text` module, but I believe all of
it is now well-covered by the `full` and `concise` tests in `ruff_db`.

I also merged this branch into
https://github.com/astral-sh/ruff/pull/20443 locally and made sure that
the API actually helps. `render_diagnostics` dropped in perfectly and
passed the tests there too.

crates/ruff_db/src/diagnostic/mod.rs

@@ -1353,7 +1353,7 @@ impl DisplayDiagnosticConfig {
     }
 
     /// Whether to show a fix's availability or not.
-    pub fn show_fix_status(self, yes: bool) -> DisplayDiagnosticConfig {
+    pub fn with_show_fix_status(self, yes: bool) -> DisplayDiagnosticConfig {
         DisplayDiagnosticConfig {
             show_fix_status: yes,
             ..self
@@ -1374,12 +1374,20 @@ impl DisplayDiagnosticConfig {
     /// availability for unsafe or display-only fixes.
     ///
     /// Note that this option is currently ignored when `hide_severity` is false.
-    pub fn fix_applicability(self, applicability: Applicability) -> DisplayDiagnosticConfig {
+    pub fn with_fix_applicability(self, applicability: Applicability) -> DisplayDiagnosticConfig {
         DisplayDiagnosticConfig {
             fix_applicability: applicability,
             ..self
         }
     }
+
+    pub fn show_fix_status(&self) -> bool {
+        self.show_fix_status
+    }
+
+    pub fn fix_applicability(&self) -> Applicability {
+        self.fix_applicability
+    }
 }
 
 impl Default for DisplayDiagnosticConfig {

crates/ruff_db/src/diagnostic/render.rs

@@ -2618,7 +2618,7 @@ watermelon
         /// Show fix availability when rendering.
         pub(super) fn show_fix_status(&mut self, yes: bool) {
             let mut config = std::mem::take(&mut self.config);
-            config = config.show_fix_status(yes);
+            config = config.with_show_fix_status(yes);
             self.config = config;
         }
 
@@ -2632,7 +2632,7 @@ watermelon
         /// The lowest fix applicability to show when rendering.
         pub(super) fn fix_applicability(&mut self, applicability: Applicability) {
             let mut config = std::mem::take(&mut self.config);
-            config = config.fix_applicability(applicability);
+            config = config.with_fix_applicability(applicability);
             self.config = config;
         }