reflect: add support for DeepEqual

The implementation has been mostly copied from the Go reference
implementation with some small changes to fit TinyGo.

Source: https://github.com/golang/go/blob/77a11c05d6a6f766c75f804ea9b8796f9a9f85a3/src/reflect/deepequal.go

In addition, this commit also contains the following:

  - A set of tests copied from the Go reflect package.
  - An increased stack size for the riscv-qemu and hifive1-qemu targets
    (because they otherwise fail to run the tests). Because these
    targets are only used for testing, this seems fine to me.

targets/hifive1-qemu.json

@@ -2,6 +2,7 @@
 	"inherits": ["fe310"],
 	"build-tags": ["hifive1b", "qemu"],
 	"serial": "uart",
+	"default-stack-size": 4096,
 	"linkerscript": "targets/hifive1-qemu.ld",
 	"emulator": ["qemu-system-riscv32", "-machine", "sifive_e", "-nographic", "-kernel"]
 }

targets/riscv-qemu.json

@@ -2,6 +2,7 @@
 	"inherits": ["riscv32"],
 	"features": "+a,+c,+m,-relax,-save-restore",
 	"build-tags": ["virt", "qemu"],
+	"default-stack-size": 4096,
 	"linkerscript": "targets/riscv-qemu.ld",
 	"emulator": ["qemu-system-riscv32", "-machine", "virt", "-nographic", "-bios", "none", "-kernel"]
 }