[libc][math][c++23] Add {nearbyint,rint,lrint,llrint,lround,llround}bf16 math functions (#153882)

This PR adds the following basic math functions for BFloat16 type along
with the tests:
- nearbyintbf16
- rintbf16
- lrintbf16
- llrintbf16
- lroundbf16
- llroundbf16

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Signed-off-by: Krishna Pandey <kpandey81930@gmail.com>
GitOrigin-RevId: 60743358d15f19b89e3ef5daa1b28e7b1bef453e
45 files changed