fix: centering block math (#9946)

Similar to `inlineCode` and `blockCode`, MFM provides two types of formula syntax, `mathInline` and `mathBlock` (I'm curious why these aren't called `inlineMath`/`blockMath`, but oh well)

Other platforms, like GitHub, **Math**todon, my blog, etc., also support these two types of formula representation, and math blocks are centered on (maybe) all such platforms.

![](https://cdn.discordapp.com/attachments/823878222897741868/1101837026304720997/2023-04-29_201943.png)

But Calckey (Misskey v12) don't center math blocks. I'd say this is a bug, and this makes `blockMath` useless (it's just `inlineMath` in a new line).

![](https://cdn.discordapp.com/attachments/823878222897741868/1101837026027917342/2023-04-29_202008.png)

So I fixed this.

![](https://cdn.discordapp.com/attachments/823878222897741868/1101837183574355978/2023-04-29_202854.png)

Co-authored-by: naskya <m@naskya.net>
Reviewed-on: https://codeberg.org/calckey/calckey/pulls/9946
Co-authored-by: naskya <naskya@noreply.codeberg.org>
Co-committed-by: naskya <naskya@noreply.codeberg.org>

packages/client/src/components/MkFormulaCore.vue

@@ -20,9 +20,12 @@ export default defineComponent({
 	},
 	computed: {
 		compiledFormula(): any {
-			return katex.renderToString(this.formula, {
+			const katexString = katex.renderToString(this.formula, {
 				throwOnError: false,
 			} as any);
+			return this.block
+				? `<div style="text-align:center">${katexString}</div>`
+				: katexString;
 		},
 	},
 });