RFR: 8311216: DataURI can lose information in some charset environments

[Michael Strauß]

DataURI uses the following implementation to decode the percent-encoded payload of a "data" URI:


...
String data = uri.substring(dataSeparator + 1);
Charset charset = Charset.defaultCharset();
...
URLDecoder.decode(data.replace("+", "%2B"), charset).getBytes(charset)


This approach only works if the charset that is passed into `URLDecoder.decode` and `String.getBytes` doesn't lose information when converting between `String` and `byte[]` representations, as might happen in a US-ASCII environment.

This PR solves the problem by not using `URLDecoder`, but instead simply decoding percent-encoded escape sequences as specified by RFC 3986, page 11.

**Note to reviewers**: the failing test can only be observed when the JVM uses a default charset that can't represent the payload, which can be enforced by specifying the `-Dfile.encoding=US-ASCII` VM option.

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Commit messages:
 - Don't use URLDecoder in DataURI
 - Failing test

Changes: https://git.openjdk.org/jfx/pull/1165/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1165&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311216
  Stats: 105 lines in 2 files changed: 93 ins; 3 del; 9 mod
  Patch: https://git.openjdk.org/jfx/pull/1165.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1165/head:pull/1165

PR: https://git.openjdk.org/jfx/pull/1165