Strict mode for JSON parsing (#2323)

* Feat #6: Add strict flag to Gson and GsonBuilder

* Test #2: Add failing tests for capitalized keywords

* Feat #2: JsonReader does not read (partially) capitalized keywords if strict mode is used

* Feat #3: Added implementation and tests for JSONReader not accepting specific escape sequence representing in strict mode

* Test #3: Simplify test cases by removing unnecessary array

* Feat #3: Improve error by including the illegal character

* Feat #5: JsonReader does not allow unespaced control flow characters in strict mode

* Test #5: Test unespaced control flow characters in strict mode

* Feat #4: Disallow espaced newline character in strict mode

* Test #4: Add tests for (dis)allowing newline character depensding on strictness

* Test #5: Test case for unescaped control char in non-strict mode

* Test #2: Simplify test cases

* Feat #13: Change leniency API to Strictness enum in JsonReader, Gson, and GsonBuilder

* Feat #15: Change JsonWriter API to also use Strictness

* Test #15: Test Strictness in JsonWriter API

* Doc #15: Add and update documentation for Strictness in JsonWriter API

* refactor #12: Fixed typos and empty catch brackets in tests

* refactor #12: Resolved importing wildcards, made some lines adhere to Google java style

* #5 Add test case for unescaped control characters

* Feat #5: add new lines to make JsonReader able to detect unescaped control characters (U+0000 through U+001F) and throw exceptions.

* Feat #5: add new lines to make JsonReader able to detect unescaped control characters (U+0000 through U+001F) and throw exceptions.

* Test #11: Added two tests for testing implementation of control character handling in strict mode and moved the implementation to nextQuotedValue

* Test #11: Added two tests for testing implementation of control character handling in strict mode and moved the implementation to nextQuotedValue

---------

Co-authored-by: LMC117 <2295699210@qq.com>
Co-authored-by: Marten Voorberg <martenvoorberg@gmail.com>

* Doc #17: Add and change javadoc of public methods

* Doc #17: Update JavaDoc in JsonReader and Strictness

* Doc #17: Update JavaDoc in Gson and GsonBuilder

* Test #34: Add tests for setting strictness through GsonBuilder

* Fix: Add Fix broken test

* Fix: Invalid JavaDoc in Gson.java

* Doc #17: update outdated javadoc

* #37: Resolve more PR feedback

* Fix #37: Resolve various PR comments

* Fix #37: Resolve various PR comments

* Refactor #35: Refactor JsonReader#peekKeyword to reduce the amount of strictness checks (#39)

* Doc #40: Update JavaDoc based on PR feedback

* Doc #40: Update old RFC in GsonBuilder documentation

* Doc #40: Fix formatting error in JavaDoc

* Doc #40: Add tests for setting strictness and lenient to JsonReaderTest

* Test #43: Changed tests to make use of assertThrows

* test #43: Changed tests to make use of assertThrows as per feedback

* Test #43: Update JsonWriterTest#testStrictnessNull to use assertThrows

* Test #43: Update JsonWriterTest#testStrictnessNull to use assertThrows

* test #43: Resolve PR recommendations

* Test #43: Mini change to TC

* Test #43: Mini change to TC

---------

Co-authored-by: Marten Voorberg <martenvoorberg@gmail.com>

* doc #46: Resolved comments in main PR

* Feat #45: Change Gson.fromJson and Gson.toJson to be strict when the provided writer/reader is strict

* Fix #45: Small type

* Update gson/src/test/java/com/google/gson/stream/JsonReaderTest.java

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* Fix #45: Resolve various comments by Marcono1234

* Update gson/src/main/java/com/google/gson/GsonBuilder.java

Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

* Fix #45: Resolve various comments by Marcono1234

* Fix #45: Resolve various comments by eamonmcmanus

* Strictness mode follow-up

* Update Troubleshooting.md and Gson default lenient mode documentation

* Always use GSON strictness when set.

* Rename Strictness.DEFAULT to Strictness.LEGACY_STRICT

* Update JavaDoc with new strictness functionality

* Replace default with legacy strict for JsonReader javadoc

* Add JSONReader test cases for U2028 and U2029

* Refactor JSONReader#peekKeyWord() based on @eamonmcmanus's suggestion

* Deprecate setLenient in favor of setStrictness

---------

Co-authored-by: Carl Peterson <unknown>
Co-authored-by: Gustaf Johansson <gustajoh@kth.se>
Co-authored-by: gustajoh <58432871+gustajoh@users.noreply.github.com>
Co-authored-by: LMC117 <2295699210@qq.com>
Co-authored-by: Marcono1234 <Marcono1234@users.noreply.github.com>

gson/src/main/java/com/google/gson/GsonBuilder.java

@@ -535,6 +535,7 @@ public GsonBuilder setFormattingStyle(FormattingStyle formattingStyle) {
    */
   @Deprecated
   @CanIgnoreReturnValue
+  @Deprecated
   public GsonBuilder setLenient() {
     strictness = Strictness.LENIENT;
     return this;

gson/src/main/java/com/google/gson/stream/JsonReader.java

@@ -976,8 +976,7 @@ public double nextDouble() throws IOException {
     peeked = PEEKED_BUFFERED;
     double result = Double.parseDouble(peekedString); // don't catch this NumberFormatException.
     if (strictness != Strictness.LENIENT && (Double.isNaN(result) || Double.isInfinite(result))) {
-      throw syntaxError(
-          "JSON forbids NaN and infinities: " + result);
+      throw syntaxError("JSON forbids NaN and infinities: " + result);
     }
     peekedString = null;
     peeked = PEEKED_NONE;