[libc][math][c23] Implement C23 math function asinpif16 (#146226)

The function is implemented using the following Taylor series that's
generated using [python-sympy](https://www.sympy.org/en/index.html), and
it is very accurate for |x| $$\in [0, 0.5]$$ and has been verified using
Geogebra. The range reduction is used for the rest range (0.5, 1].

$$
\frac{\arcsin(x)}{\pi} \approx 
\begin{aligned}[t]
    &  0.318309886183791x  \\
    & + 0.0530516476972984x^3 \\
    & + 0.0238732414637843x^5 \\
    & + 0.0142102627760621x^7 \\
    & + 0.00967087327815336x^9 \\
    & + 0.00712127941391293x^{11} \\
    & + 0.00552355646848375x^{13} \\
    & + 0.00444514782463692x^{15} \\
    & + 0.00367705242846804x^{17} \\
    & + 0.00310721681820837x^{19} + O(x^{21})
\end{aligned}
$$

## Geogebra graph

![28-06-2025-1913-eDP-1](https://github.com/user-attachments/assets/f70818e1-1b34-406e-962a-a30fdc909f18)

Closes #132210

libc/include/math.yaml

@@ -79,6 +79,13 @@ functions:
     arguments:
       - type: _Float16
     guard: LIBC_TYPES_HAS_FLOAT16
+  - name: asinpif16
+    standards:
+      - stdc
+    return_type: _Float16
+    arguments:
+      - type: _Float16
+    guard: LIBC_TYPES_HAS_FLOAT16
   - name: atan
     standards:
       - stdc