RFR: 8373727: New XBM images parser regression: only the first line of the bitmap array is parsed [v2]

[Damon Nguyen]

> There were three concerns with the previous changes to `XbmImageDecoder`.
> 1. Only the first line of the bit array was read.
> 2. The regex was incorrect because it used `[]` instead of `()` for some grouping.
> 3. The ordering of the width and height in the xbm file was too strict and had to be width first, then height.
> 
> To fix these issues, I have:
> 1. Used a StringBuilder to append lines of the bit array to parse the entire array at once. This required changing the parsing loop and moving some code.
> 2. Updated the regex to capture starting whitespace, optionally start with `0x`, include all chars/digits/punctuation (minus `,` and `};`) instead of just valid hex digits, and end with either `,` or `};`. This also allows for incorrect hex values such as `0x12345abcde` to be detected since the new regex allows for multiple chars after the `0x` until the next delimiter is found. This is accounted for in the test xbm files.
> 3. Determined width or height based off of ending letters (`th` or `t`). This is similar to https://github.com/openjdk/jdk/blob/jdk-26+10/src/java.desktop/share/classes/sun/awt/image/XbmImageDecoder.java#L109-L112.
> 
> A new method is added to `XBMDecoderTest.java` to better check that the bit array parsing works. This method checks for non-empty pixel data.
> 
> A new xbm file is also added to check for the case where `0xAB+` exists in the bit array. This should be invalid, and the previous regex would allow this to pass. 
> 
> All tests pass with the new changes made here.

Damon Nguyen has updated the pull request incrementally with one additional commit since the last revision:

  Add test for empty bit array

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/29120/files
  - new: https://git.openjdk.org/jdk/pull/29120/files/8e4826c5..a7542524

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29120&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29120&range=00-01

  Stats: 16 lines in 2 files changed: 9 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/29120.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29120/head:pull/29120

PR: https://git.openjdk.org/jdk/pull/29120