Build modified streamline images

The official image from streamline does not currently work for the arm64
platform. As a temporary measure, the source code and docker build scripts
have been lifted from the official images and are used to build locally.

Some additional modifications are made to reduce overall image size, these
are documented in docker/README.md

docker/streamline-src/vendor/league/commonmark/src/Delimiter/Delimiter.php

@@ -0,0 +1,134 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the league/commonmark package.
+ *
+ * (c) Colin O'Dell <colinodell@gmail.com>
+ *
+ * Original code based on the CommonMark JS reference parser (https://bitly.com/commonmark-js)
+ *  - (c) John MacFarlane
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace League\CommonMark\Delimiter;
+
+use League\CommonMark\Node\Inline\AbstractStringContainer;
+
+final class Delimiter implements DelimiterInterface
+{
+    /** @psalm-readonly */
+    private string $char;
+
+    /** @psalm-readonly-allow-private-mutation */
+    private int $length;
+
+    /** @psalm-readonly */
+    private int $originalLength;
+
+    /** @psalm-readonly */
+    private AbstractStringContainer $inlineNode;
+
+    /** @psalm-readonly-allow-private-mutation */
+    private ?DelimiterInterface $previous = null;
+
+    /** @psalm-readonly-allow-private-mutation */
+    private ?DelimiterInterface $next = null;
+
+    /** @psalm-readonly */
+    private bool $canOpen;
+
+    /** @psalm-readonly */
+    private bool $canClose;
+
+    /** @psalm-readonly-allow-private-mutation */
+    private bool $active;
+
+    /** @psalm-readonly */
+    private ?int $index = null;
+
+    public function __construct(string $char, int $numDelims, AbstractStringContainer $node, bool $canOpen, bool $canClose, ?int $index = null)
+    {
+        $this->char           = $char;
+        $this->length         = $numDelims;
+        $this->originalLength = $numDelims;
+        $this->inlineNode     = $node;
+        $this->canOpen        = $canOpen;
+        $this->canClose       = $canClose;
+        $this->active         = true;
+        $this->index          = $index;
+    }
+
+    public function canClose(): bool
+    {
+        return $this->canClose;
+    }
+
+    public function canOpen(): bool
+    {
+        return $this->canOpen;
+    }
+
+    public function isActive(): bool
+    {
+        return $this->active;
+    }
+
+    public function setActive(bool $active): void
+    {
+        $this->active = $active;
+    }
+
+    public function getChar(): string
+    {
+        return $this->char;
+    }
+
+    public function getIndex(): ?int
+    {
+        return $this->index;
+    }
+
+    public function getNext(): ?DelimiterInterface
+    {
+        return $this->next;
+    }
+
+    public function setNext(?DelimiterInterface $next): void
+    {
+        $this->next = $next;
+    }
+
+    public function getLength(): int
+    {
+        return $this->length;
+    }
+
+    public function setLength(int $length): void
+    {
+        $this->length = $length;
+    }
+
+    public function getOriginalLength(): int
+    {
+        return $this->originalLength;
+    }
+
+    public function getInlineNode(): AbstractStringContainer
+    {
+        return $this->inlineNode;
+    }
+
+    public function getPrevious(): ?DelimiterInterface
+    {
+        return $this->previous;
+    }
+
+    public function setPrevious(?DelimiterInterface $previous): void
+    {
+        $this->previous = $previous;
+    }
+}