[Lang] Support very basic python string.format() now

[Leonz5288]

Related issue = #2396

[Leonz5288]

/format

[Leonz5288]

We support basic string format in print now. For example, code below:

import taichi as ti
ti.init()
ops = ti.field(ti.float32, shape=(1, ))
yes = ti.field(ti.int32, shape=(1, ))

@ti.kernel
def test():
    ops[0] = 3.14
    yes[0] = 3
    print('Two numbers:', ' {} and {} '.format(ops[0], yes[0]), 'and a list: ', ['q', 'w', 'e', 'r'], sep='|')
    print('round{}square{}what?{}'.format(ops[0], 123, ' wellwellwell'))

test()

Would print the result:

Two numbers:| 3.140000 and 3 |and a list: |[q, w, e, r]
round3.140000square123what? wellwellwell

[Leonz5288]

/format

[ljcc0930]

/format

[ljcc0930]

LGTM!

[CLAassistant]

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