fix: UriTemplate reserved expansion does not escape reserved chars

[cHengstler]

When using UriTemplate.expand with a reserved expansion "{+var}", a set of allowed characters must not be encoded. According to section of 3.2.3 Reserved Expansion: {+var}, unreserved and reserved character should not be escaped.

This fix adds the missing characters #[] that must not be percent encoded when using reserved expansion.

• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Fixes #1838

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[suztomo]

Memo:

1. Are the added characters (#[]) marked as the reserved set? Yes

     reserved       =  gen-delims / sub-delims
     gen-delims     =  ":" / "/" / "?" / "#" / "[" / "]" / "@"
   

2. (Todo on me) Try out this change in java-storage before merge, and see any failures.
   => [No need to review] trying new reserved characters in http client java-storage#2005

[suztomo]

@cHengstler Can you fix the lint failure?

[INFO] --- fmt-maven-plugin:2.9:check (default-cli) @ google-http-client ---
[INFO] Processed 100 files (1 non-complying).
[INFO] Processed 200 files (1 non-complying).
[INFO] Processed 216 files (2 non-complying).
Error:  Found 2 non-complying files, failing build
Error:  To fix formatting errors, run "mvn com.coveo:fmt-maven-plugin:format"
Error:  Non complying file: /home/runner/work/google-http-java-client/google-http-java-client/google-http-client/src/main/java/com/google/api/client/util/escape/PercentEscaper.java
Error:  Non complying file: /home/runner/work/google-http-java-client/google-http-java-client/google-http-client/src/test/java/com/google/api/client/http/UriTemplateTest.java

[cHengstler]

Hi @suztomo,

thanks for reviewing, linting issues should be solved now.

[suztomo]

Memo: Python's uritemplate agrees:

>>> a="-._~"; a == URITemplate("{+var}").expand(var=a)
True
>>> a=":/?#[]@!$&'()*+,;="; a == URITemplate("{+var}").expand(var=a)
True

[suztomo]

ci / lint passed.