RFR: 8281525: Enable Zc:strictStrings flag in Visual Studio build

[Daniel Jeliński]

Please review this PR that enables [Zc:strictStrings](https://docs.microsoft.com/en-us/cpp/build/reference/zc-strictstrings-disable-string-literal-type-conversion?view=msvc-170) compiler flag, which makes assigning a string literal to a non-const pointer a compile-time error.

This type of assignment is [disallowed by C++ standard since C++11](https://en.cppreference.com/w/cpp/language/string_literal). Writing to a string literal through a non-const pointer [produces a run-time error](https://docs.microsoft.com/en-us/cpp/cpp/string-and-character-literals-cpp?view=msvc-170#microsoft-specific-1).

The included code changes are trivial; I added `const` keyword to variable and parameter declarations where needed, and added explicit casts to non-const pointers where adding `const` was not feasible.

I verified that the build passes both with and without `--enable-debug`, both with VS2017 and VS2019.

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Commit messages:
 - Strict strings

Changes: https://git.openjdk.java.net/jdk/pull/7565/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7565&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281525
  Stats: 22 lines in 6 files changed: 0 ins; 0 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7565.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7565/head:pull/7565

PR: https://git.openjdk.java.net/jdk/pull/7565