Support blaming parent revisions (#62614)

Closes https://github.com/zed-industries/zed/discussions/42583

Adds more tooltip entries and `editor::BlameRevision`,
`editor::BlamePreviousRevision` actions to use.
Started to highlight gutter blame entries that belong to currently
annotated commit.


https://github.com/user-attachments/assets/ba754e0b-6431-407c-8d79-2f8b0324fde1


Release Notes:

- Supported blaming parent revisions

crates/git/src/git.rs

@@ -225,7 +225,7 @@ impl Oid {
         &self.bytes[..self.format.byte_len()]
     }
 
-    pub(crate) fn is_zero(&self) -> bool {
+    pub fn is_zero(&self) -> bool {
         self.as_bytes().iter().all(|byte| *byte == 0)
     }