style: use decl literals

This commit changes a LOT of areas of the code to use decl literals
instead of redundantly referring to the type.

These changes were mostly driven by some regex searches and then manual
adjustment on a case-by-case basis.

I almost certainly missed quite a few places where decl literals could
be used, but this is a good first step in converting things, and other
instances can be addressed when they're discovered.

I tested GLFW+Metal and building the framework on macOS and tested a GTK
build on Linux, so I'm 99% sure I didn't introduce any syntax errors or
other problems with this. (fingers crossed)

src/terminal/bitmap_allocator.zig

@@ -403,7 +403,7 @@ test "BitmapAllocator alloc sequentially" {
     const buf = try alloc.alignedAlloc(u8, Alloc.base_align, layout.total_size);
     defer alloc.free(buf);
 
-    var bm = Alloc.init(OffsetBuf.init(buf), layout);
+    var bm = Alloc.init(.init(buf), layout);
     const ptr = try bm.alloc(u8, buf, 1);
     ptr[0] = 'A';
 
@@ -429,7 +429,7 @@ test "BitmapAllocator alloc non-byte" {
     const buf = try alloc.alignedAlloc(u8, Alloc.base_align, layout.total_size);
     defer alloc.free(buf);
 
-    var bm = Alloc.init(OffsetBuf.init(buf), layout);
+    var bm = Alloc.init(.init(buf), layout);
     const ptr = try bm.alloc(u21, buf, 1);
     ptr[0] = 'A';
 
@@ -453,7 +453,7 @@ test "BitmapAllocator alloc non-byte multi-chunk" {
     const buf = try alloc.alignedAlloc(u8, Alloc.base_align, layout.total_size);
     defer alloc.free(buf);
 
-    var bm = Alloc.init(OffsetBuf.init(buf), layout);
+    var bm = Alloc.init(.init(buf), layout);
     const ptr = try bm.alloc(u21, buf, 6);
     try testing.expectEqual(@as(usize, 6), ptr.len);
     for (ptr) |*v| v.* = 'A';
@@ -478,7 +478,7 @@ test "BitmapAllocator alloc large" {
     const buf = try alloc.alignedAlloc(u8, Alloc.base_align, layout.total_size);
     defer alloc.free(buf);
 
-    var bm = Alloc.init(OffsetBuf.init(buf), layout);
+    var bm = Alloc.init(.init(buf), layout);
     const ptr = try bm.alloc(u8, buf, 129);
     ptr[0] = 'A';
     bm.free(buf, ptr);