fix(builtin.buffers): previews with specified cwd option (#3111)

Currently, the buffer name is normalized to the `cwd` option value.
This buffer name is then used as the filename, which is used as the file
path for the previewer. But if the `cwd` value is not the actual cwd,
the buffer path can no longer be found by the previewer (relative to the
true cwd).

This is fixed by adding a `path` value to the entry that's the full path
of the buffer. The previewer will then use this full path to find the
file to preview.

(cherry picked from commit ccaeeb5af5)

lua/telescope/make_entry.lua

@@ -615,9 +615,8 @@ function make_entry.gen_from_buffer(opts)
   end
 
   return function(entry)
-    local bufname = entry.info.name ~= "" and entry.info.name or "[No Name]"
-    -- if bufname is inside the cwd, trim that part of the string
-    bufname = Path:new(bufname):normalize(cwd)
+    local filename = entry.info.name ~= "" and entry.info.name or nil
+    local bufname = filename and Path:new(filename):normalize(cwd) or "[No Name]"
 
     local hidden = entry.info.hidden == 1 and "h" or "a"
     local readonly = vim.api.nvim_buf_get_option(entry.bufnr, "readonly") and "=" or " "
@@ -640,8 +639,8 @@ function make_entry.gen_from_buffer(opts)
       value = bufname,
       ordinal = entry.bufnr .. " : " .. bufname,
       display = make_display,
-
       bufnr = entry.bufnr,
+      path = filename,
       filename = bufname,
       lnum = lnum,
       indicator = indicator,