feat(NcIcon): add a generic component for icons

Signed-off-by: Grigorii K. Shartsev <me@shgk.me>

src/components/NcIcon/NcIcon.vue

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+<!--
+  - SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+  - SPDX-License-Identifier: AGPL-3.0-or-later
+-->
+
+<docs>
+## General
+
+A component to render an icons. It can render:
+- A Vue component icon like `vue-material-design-icons/Account.vue`
+- An SVG icon like `@mdi/svg/svg/account.svg`
+- A path icon like `@mdi/js/account.js`
+- An URL icon like `https://path/to/icon.svg` or `data:image/svg+xml;base64,...`
+- A class icon like `icon-account` (not recommended)
+
+```vue
+<script>
+import IconAccountComp from 'vue-material-design-icons/Account.vue'
+import IconAccountSvg from '@mdi/svg/svg/account.svg?raw'
+import { mdiAccount } from '@mdi/js'
+
+export default {
+  setup() {
+    return { IconAccountComp, IconAccountSvg, mdiAccount }
+  },
+}
+</script>
+
+<template>
+    <div>
+        <NcIcon :icon="IconAccountComp" />
+        <NcIcon :icon="IconAccountSvg" />
+        <NcIcon :icon="mdiAccount" />
+        <NcIcon icon="icon-user-white" />
+    </div>
+</template>
+```
+</docs>
+
+<script setup>
+import { computed } from 'vue'
+import { useIcon } from './useIcon.ts'
+import NcIconSvgWrapper from '../NcIconSvgWrapper/NcIconSvgWrapper.vue'
+
+const props = defineProps({
+	icon: { type: [Object, String], required: true },
+	size: { type: [Number, String], default: 20 },
+	inline: { type: Boolean, default: false },
+})
+
+const normalizedIcon = useIcon(() => props.icon)
+const normalizedSize = computed(() => typeof props.size === 'number' ? `${props.size}px` : props.size)
+</script>
+
+<template>
+	<component :is="icon" v-if="normalizedIcon.type === 'component'" :size="normalizedSize" />
+	<NcIconSvgWrapper v-else-if="normalizedIcon.type === 'svg'" :svg="normalizedIcon.icon" :inline="inline" />
+	<NcIconSvgWrapper v-else-if="normalizedIcon.type === 'path'" :path="normalizedIcon.icon" :inline="inline" />
+	<span v-else-if="normalizedIcon.type === 'class'"
+		class="icon"
+		:class="[normalizedIcon.icon, { inline }]"
+		:style="'--icon-size: ' + normalizedSize"
+		aria-hidden="true" />
+	<span v-else-if="normalizedIcon.type === 'url'"
+		class="icon icon-url"
+		:class="{ inline }"
+		:style="`background-image: url('${normalizedIcon.icon}')`"
+		aria-hidden="true" />
+</template>
+
+<style scoped>
+.icon {
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    min-width: var(--default-clickable-area);
+    min-height: var(--default-clickable-area);
+    height: var(--icon-size);
+	width: var(--icon-size);
+
+    &.inline {
+		display: inline-flex;
+		min-width: fit-content;
+		min-height: fit-content;
+		vertical-align: text-bottom;
+	}
+}
+</style>

src/components/NcIcon/normalizeIcon.ts

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+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+import type { Component } from 'vue'
+
+export type IconComponent = Component
+export type IconPath = `M${number}${string}`
+export type IconSvg = `<svg${string}>${string}</svg>`
+export type IconUrl = `http://${string}` | `https://${string}` | `data:${string}`
+export type IconClass = `icon-${string}`
+export type IconGeneral = IconComponent | IconPath | IconClass | IconSvg | IconUrl
+
+export type IconNormalized = { type: 'component', icon: IconComponent }
+    | { type: 'path', icon: IconPath }
+    | { type: 'svg', icon: IconSvg }
+    | { type: 'url', icon: IconUrl }
+    | { type: 'class', icon: IconClass }
+    | { type: 'unknown', icon: IconGeneral }
+
+/**
+ *
+ * @param icon - Icon in any supported format
+ */
+export function normalizeIcon(icon: IconGeneral): IconNormalized {
+	if (typeof icon === 'object' || typeof icon === 'function') {
+		return { type: 'component', icon: icon as IconComponent }
+	}
+	if (icon.startsWith('<svg')) {
+		return { type: 'svg', icon: icon as IconSvg }
+	}
+	if (icon.startsWith('M')) {
+		return { type: 'path', icon: icon as IconPath }
+	}
+	if (icon.startsWith('http://') || icon.startsWith('https://') || icon.startsWith('data:')) {
+		return { type: 'url', icon: icon as IconUrl }
+	}
+	if (icon.startsWith('icon-')) {
+		return { type: 'class', icon: icon as IconClass }
+	}
+	return { type: 'unknown', icon: icon as IconGeneral }
+}

src/components/NcIcon/useIcon.ts

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+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+import type { ComputedRef } from 'vue'
+import type { MaybeRefOrGetter } from '@vueuse/core'
+import type { IconGeneral, IconNormalized } from './normalizeIcon.ts'
+import { computed } from 'vue'
+import { toValue } from '@vueuse/core'
+import { normalizeIcon } from './normalizeIcon.ts'
+
+/**
+ * Reactive normalizeIcon
+ * @param icon - Icon in any supported format
+ */
+export function useIcon(icon: MaybeRefOrGetter<IconGeneral>): ComputedRef<IconNormalized> {
+	return computed(() => normalizeIcon(toValue(icon)))
+}