feat: use scr for script letters in math mode

`scr` is first added in typst v0.14.0.

See https://typst.app/docs/reference/math/variants/#functions-scr for
more information.

Author: johanvx

README.md

@@ -13,6 +13,8 @@ The following limitations are also annotated in the [document][latest-release].
 - [x] ~Script letters, such as $\mathscr{P}$ form `\mathscr{P}`, are unavailable.~
       It's possible to get script letters like $\mathscr{P}$ from `cal(P)` by changing the [`stylistic-set` of the `text()` function].
       The stylistic set to apply is font-specific, so it's necessary to consult the font to know which set is desired.
+      As from `typst v0.14.0`, $\mathscr{P}$ can be easily obtained with `scr(P)`.
+      See `scr` for more information.
 - [x] ~Greek letter $\varsigma$ `\u{03C2}` from `\varsigma` is not defined as a symbol and should probably be defined as `sigma.alt`.~
       `sigma.alt` is available as from `typst v0.5.0`.
 - [x] $\emptyset$ from `\emptyset` is available in Typst as `nothing`, while $\varnothing$ from `\varnothing` is not.

undergradmath.typ

@@ -154,8 +154,10 @@ Use as in `$cal(A)$`.
 
 $ cal(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z) $
 
-#show math.equation: set text(stylistic-set: 1)
-Get script letters, such as $cal(P)$ from `$cal(P)$`, by changing the `stylistic-set` parameter of `text()` to the corresponding set.
+// #show math.equation: set text(stylistic-set: 1)
+// Get script letters, such as $cal(P)$ from `$cal(P)$`, by changing the `stylistic-set` parameter of `text()` to the corresponding set.
+Get script letters by using `scr`, such as $scr(P)$ from `$scr(P)$`.
+See #link("https://typst.app/docs/reference/math/variants/#functions-scr")[`scr`] for more information.
 
 = Greek
 #align(