Workaround microsoft/terminal#16606 (oven-sh#8506)

Fixes oven-sh#8504

src/bun.js/webcore.zig

@@ -244,8 +244,7 @@ pub const Prompt = struct {
         bun.Output.flush();
 
         // 7. Pause while waiting for the user's response.
-        var stdin = std.io.getStdIn();
-        var reader = stdin.reader();
+        const reader = bun.buffered_stdin.reader();
 
         const first_byte = reader.readByte() catch {
             // 8. Let result be null if the user aborts, or otherwise the string

src/bun.zig

@@ -2453,3 +2453,9 @@ pub fn getUserName(output_buffer: []u8) ?[]const u8 {
     copy(u8, output_buffer[0..size], user[0..size]);
     return output_buffer[0..size];
 }
+
+/// This struct is a workaround a Windows terminal bug.
+/// TODO: when https://github.com/microsoft/terminal/issues/16606 is resolved, revert this commit.
+pub var buffered_stdin = std.io.BufferedReader(4096, std.fs.File.Reader){
+    .unbuffered_reader = std.fs.File.Reader{ .context = .{ .handle = if (Environment.isWindows) undefined else 0 } },
+};

src/cli/init_command.zig

@@ -39,7 +39,7 @@ pub const InitCommand = struct {
 
         Output.flush();
 
-        var input = try std.io.getStdIn().reader().readUntilDelimiterAlloc(alloc, '\n', 1024);
+        var input = try bun.buffered_stdin.reader().readUntilDelimiterAlloc(alloc, '\n', 1024);
         if (strings.endsWithChar(input, '\r')) {
             input = input[0 .. input.len - 1];
         }

src/main.zig

@@ -39,6 +39,8 @@ pub fn main() void {
         bun.win32.STDERR_FD = bun.toFD(std.io.getStdErr().handle);
         bun.win32.STDIN_FD = bun.toFD(std.io.getStdIn().handle);
 
+        bun.buffered_stdin.unbuffered_reader.context.handle = std.io.getStdIn().handle;
+
         const w = std.os.windows;
 
         // https://learn.microsoft.com/en-us/windows/console/setconsoleoutputcp